No mention that both sets of primaries come from the biology of the average human eye, and other animals might be better served by other colors? Ok, yeah, that's not really relevant to the point the article was actually getting to, but I think it's important to remember. There's nothing magical about those colors. They effectively stimulate color receptors in our eyes such that our brains interpret the input in ways that can be combined to cover a pretty large gamut of the full range our eyes can perceive.
But as for what the article actually does focus on, I absolutely agree. You can create some really striking art by restricting your gamut to the range you can cover with a particular set of pigments.
In addition to this, there will always be 2 sets of "primary" colors for a given eye: Additive and Subtractive.
Additive primary colors are necessary when you have no light, and need to create color. Think a black screen, and you are creating colors with RGB pixels.
Subtractive primary colors are necessary when you have full-spectrum (white) light and need to filter down to a single color.
Other "primary" colors, such as the red, blue, yellow pigment primaries we learned in Kindergarten exist because pigments historical couldn't be created perfectly, and those "primaries" are the best way of getting the most colors, but still have a very limited (by comparison) gamut.
Yes, one challenge with defining Subtractive primaries is that they are dependent on the white point of the "white" light source (e.g. D65 vs D50). While this seems inconvenient, it's worth noting that the apparent color of greys for Additive primaries is also dependent on surrounding illumination.
So primaries are useful for generating roughly orthogonal changes in perceived color, but they don't tell you how they will be perceived in absolute terms without knowing surrounding illumination. In the simplest case, asking if something is bright (even without color) is impossible without knowing the surroundings.
I think that understanding how eyes and light work is very informative on this subject.
Why are there 3 primary colors (regardless of which 3 you pick)? That has nothing to do with the nature of light, and everything to do with the fact that humans see light using 3 distinct frequency response curves [0]. This means that humans perceive color as a 3 dimensional space; and the role of the primary colors is to pick a point in this space by selectively stimulating or masking the 3 response curves. In a world of pure linear algebra, almost any 3 colors would do, but physical reality limits how ideally we can mix them; and how much light they can emit/mask.
Further, the 3 response curves are overlapping, so there is no set of ideal colors that would let you actually control the 3 curves independently.
[0] At least for color perception in a typical human.
The linear algebra argument for almost any three colors only works if you can have negative intensities. I don't know how to do that with stimulation of photoreceptors, so I don't think that applies here.
Besides having 3 primary kinds of photoreceptors, there are additional complications caused by the initial processing of the color information in the visual system.
Besides the 3 primary color sensations from the red, green & blue receptors, there are a few dedicated detectors for some colors.
Yellow is detected when red is equal to green and both have a high enough brightness. White is detected when red, green & blue are equal and all have a high enough brightness. While black could be detected later, by the lack of information on the other channels, it seems that it also has a dedicated detector.
This gives 6 primary color sensations, where the colors are not perceived as a mixture of colors, like it is the case for orange, blue-green, violet, purple or gray. Presumably these 6 colors correspond to separate outputs of the initial color processing stage of the visual system.
I do not know whether this is true, but I believe that there also exists a dedicated detector for the color brown. While brown is just orange with low brightness, the "brown" sensation is very distinct and very unlike the differences perceived between e.g. dark red and light red, dark green and light green or dark blue and light blue, where the differences are perceived to be only in quantity, not in quality.
A dedicated detector for brown makes sense, because important things in the environment are brown, e.g. the ground is brown in most cases, because it is composed of a mixture of white oxides with red, yellow and black oxides of iron and manganese. Also wood is frequently brown and also many mammals are brown.
I am surprised that the Purkinje effect and the degree of illumination are not mentioned. For example, should the primary colors be shifted depending on illumination?
"Artists traditionally" is doing a bit of heavy lifting here. Neither artists nor art teachers explain a concept that all colours can be mixed from RBY primaries for the simple reason that the jig is up the moment they start painting. Rather artists very loosely describe these colours as primaries as a starting point to the concept of mixing colour.
In actual art classes they teach the colour wheel, which usually leads to around 6 colours being used for general painting in addition to white and other colours to darken. They're also not super fixated on what these colours should be specifically instead using terms such as "warm red and cool red", "warm blue and cool blue" etc. There is always a constant recognition that these will still present a limited gamut and that may be a deliberate artistic choice.
There is also an understanding that additional paints may be needed for getting a stronger colour or simply the convenience of not having to mix so much. This thinking continues through into professional printing hence the Pantone system or more interestingly with certain Epson printers that can include ink tanks specifically for violet, green, orange (amongst many others) - where the software will do the heavy lifting of blending these colours with the CMY model to produce a vivid gamut.
On the topic of "Key". Key is the pigment used to introduce detail and tone. For a two colour artwork the Key could simply be the darker of the two shades. We know it as black, but in some print processes it's an imperfect black-like colour that blends well with CMY to produce detail. Again in those Epson printers mentioned earlier, multiple blacks are used depending if it is to be used for creating detail in the coloured areas or simply as a block of black.
You can distort this shape into a circle but you lose the geometric relationship between chromaticities—two points an equal distance along the circumference of the color wheel don’t necessarily feel “as different” from each other.
Even this is a simplification. The color space you see is three-dimensional, because that is the physical reality of how your eyes work. Any representation of the color space in two dimensions involves choosing a projection that distorts reality.
Sort of. Your photoreceptors are sensitive to overlapping frequencies, which means they’re not linearly independent and therefore cannot form the basis vectors of a 3D space.
CIE XYZ accounts for this by projecting SML excitations down to a 2D plane (XY) and making the third dimension a color-independent luminosity (Z). Since it’s luminosity-independent, the 2D slice is directly analogous to the color wheel.
Related is that English has 11 basic color terms: black, white, red, green, yellow, blue, brown, orange, pink, purple, and gray. As a result, trying to teach cyan and magenta as primary colors will be much harder than teaching blue and red as primary colors.
Eliminating from your 11-item list the words that cannot designate saturated colors, i.e. black, white, brown, pink and gray, there remain 6 words for saturated colors: red, orange, yellow, green, blue and purple.
Besides these 6 words, 2 more words are useful for naming saturated colors. The use of the word "violet" is widespread enough that it should be added to the list as a basic English color term.
The distinction between violet and purple is that while both are mixtures of red and blue, violet contains a small enough amount of red that it can be matched by a monochromatic color in the violet range of the spectrum, while purple contains an amount of red that is great enough so that it can be matched only by a mixture of monochromatic red with monochromatic blue.
A word is needed for the blue-green color. Cyan is a misnomer that should be avoided, but "turquoise" is a word that has been used in English for many centuries for designating the blue-green color (and which is used for the same purpose in many other European languages, all of which have borrowed the word from French, like also English). "Teal" is another synonym for "blue-green", which has been introduced in the 20th century.
There have been many misunderstandings about the words used by Isaac Newton for his circle of colors, but I believe that when his words are interpreted correctly, he was right.
Isaac Newton has divided the saturated colors into 8 colors: red, orange, yellow, green, blew or blue, indico or indigo, violet and purple. The first 7 of these were classified as prismatic colors, i.e. as monochromatic colors.
Isaac Newton spelled blue as both "blew" and "blue", and also indigo was spelled as both "indico" and "indigo". While the meaning of the other color words is not ambiguous, the meaning of these 2 words is not clear.
The words used by Isaac Newton were the names of some paints, whose hue he compared with the colors obtained by the dispersion of the solar light. The "indico" paint was presumably made with the indigo pigment, so it must have been blue.
The "blew" or "blue" of Isaac Newton was the color of the "blue Bise" paint. "Bise" is more frequently spelled "bice" and it was the name of a paint based on copper carbonate. Depending on the exact details of its method of preparation, such a paint will contain a mixture of malachite and azurite pigments, so it might have any hue between green and blue. We do not know who was Newton's paint supplier or any other details about the paint used by Newton, so it cannot be known for sure which was the real color of Newton's "blew".
Nevertheless I assume that Newton's "blue Bise" was actually a blue-green paint, because only in this case Newton's classification of the saturated colors will make perfect sense, because blue-green and blue are distinctive enough to deserve to have their own names.
So translated into modern English, the 8 saturated colors of Isaac Newton would be: red, orange, yellow, green, turquoise, blue, violet and purple. This classification remains right.
While you are right, "magenta" is just a fancy synonym for "purple". It might have been chosen instead of "purple" because the traditional word could be applied to colors having various proportions of red and blue, while "magenta" is intended to convey that the amounts of red and blue are equal. However all the traditional color names, like "red", "green" or "blue" refer to wide ranges of hues, not to a precise hue, so there was really no good reason for the use of the word "magenta".
"Cyan" is a very bad word choice caused by confusions in the translations of Ancient Greek texts made by philologists ignorant of chemistry and mineralogy. In Ancient Greek, "cyan" meant pure blue, not blue-green. More precisely, it was the color of the ultramarine blue pigment, the most expensive blue pigment at that time, which was imported from the present territory of Afghanistan and for which the name "ku-wa-no" was already used by the Hittites, a millennium before the Greeks. Nowadays ultramarine blue is still used as a pigment, but it is made synthetically, so its cost is a small fraction of what it was before the 19th century.
Before the use of "cyan" has started, the color name "blue-green" had been used for a very long time. Similarly, "orange" is a relatively new English word, but the color had been mentioned for many centuries, as "red-yellow" or "yellow-red".
So the awareness of distinct hues is not necessarily limited to the set of simple color words, because most languages have used compound words to name the hues for which they did not have a simple word.
Other languages have used the names of well-known colored objects to distinguish the hues that did not have distinct names. For instance, in Latin the word for "red" was used for both red colors and purple colors. When Latin speakers wanted to specify whether something was red or purple, they would say "red like the kermes (red) dye" or "red like the purple dye" (the word "purple" as a color name comes from the latter expression). Similarly, in Latin the word for green meant either green or blue-green. To distinguish the 2 colors, a Latin speaker would say "green like grass" or "green like leaves" or "green like emeralds" for expressing "green" and "green like the littoral sea" or "green like beryls" or "green like turquoise gems" for expressing "blue-green". So they were well aware about the differences between these colors, even if they did not have distinct words for them.
Purple is attested as a color name in English for about 600 years.
Before that, it has been used as a color name in various languages that have borrowed it from Latin or directly from Greek, where it had been used for about 3000 years or more.
Magenta has been used as a color name in English since 1860, "named in honor of the Battle of Magenta in Italy, where the French and Sardinians defeated the Austrians in 1859".
Initially, magenta was not a generic color name, like today, but it designated a certain cheap aniline dye, of purple color.
So purple cannot be considered a synonym for the neologism "magenta". Magenta could be considered as a certain specific shade of purple, except that during the time it has been applied to different dyes, depending on the evolution of dye technology, so the word "magenta" has not meant always the same color, but at most a range of purple colors that was never defined precisely.
One of the things I love about “Contact” is that the contact mechanism chosen by the aliens was so close to what I guessed aliens would use when I first learned about SETI.
Decimal is not universal. Not seconds, not meters, not sound frequencies used for communication, not colors. Our sky isn’t blue, it’s purple. Ask any bee and they’ll tell you. But hydrogen glows at very specific colors and that only changes if you are moving fast enough.
The fundamental colors are the colors of the elements and, I might argue, their oxides. As reflected by light or when they incandesce. Gold. Rust. Arsenic green. Carbon black. Maybe the emission bands of noble gases, though those are hardly every day items.
(If I were a very clever alien though, and I discovered exotic states of matter where the elements behaved differently, and I only wanted to talk to other very clever aliens, I might use those instead to talk over the heads of the younger or dumber species, which is why I stopped contributing to SETI. We are looking under the wrong rocks, IMO).
The most common green color from excited nitrogen molecules going back to normal by emitting 557.7 nanometer photons. Oxygen makes 650 nm red, and the 427.8 nm blue is from nitrogen ions.
It is easier to understand additive primaries through a chromaticity diagram. You can form colors by mixing the primaries, and the gamut is determined by the hull of the primaries. Obviously you need at least three of them to enclose a space.
There’s more to colour perception than the cone cells in the retina. There’s also the opponent process in the visual cortex, which is where preschool primary colours come from. https://en.wikipedia.org/wiki/Opponent_process
As somebody living in central europe I have never in my life met somebody who claimed that yellow is a primary color. The fact that this could be a thing puzzles me beyond believe.
No mention that both sets of primaries come from the biology of the average human eye, and other animals might be better served by other colors? Ok, yeah, that's not really relevant to the point the article was actually getting to, but I think it's important to remember. There's nothing magical about those colors. They effectively stimulate color receptors in our eyes such that our brains interpret the input in ways that can be combined to cover a pretty large gamut of the full range our eyes can perceive.
But as for what the article actually does focus on, I absolutely agree. You can create some really striking art by restricting your gamut to the range you can cover with a particular set of pigments.
In addition to this, there will always be 2 sets of "primary" colors for a given eye: Additive and Subtractive.
Additive primary colors are necessary when you have no light, and need to create color. Think a black screen, and you are creating colors with RGB pixels.
Subtractive primary colors are necessary when you have full-spectrum (white) light and need to filter down to a single color.
Other "primary" colors, such as the red, blue, yellow pigment primaries we learned in Kindergarten exist because pigments historical couldn't be created perfectly, and those "primaries" are the best way of getting the most colors, but still have a very limited (by comparison) gamut.
Yes, one challenge with defining Subtractive primaries is that they are dependent on the white point of the "white" light source (e.g. D65 vs D50). While this seems inconvenient, it's worth noting that the apparent color of greys for Additive primaries is also dependent on surrounding illumination.
So primaries are useful for generating roughly orthogonal changes in perceived color, but they don't tell you how they will be perceived in absolute terms without knowing surrounding illumination. In the simplest case, asking if something is bright (even without color) is impossible without knowing the surroundings.
> There will always be 2 sets of "primary" colors for a given eye: Additive and Subtractive.
If your eye only has two types of cone cells then your additive and subtractive primaries are the same ;)
I think that understanding how eyes and light work is very informative on this subject.
Why are there 3 primary colors (regardless of which 3 you pick)? That has nothing to do with the nature of light, and everything to do with the fact that humans see light using 3 distinct frequency response curves [0]. This means that humans perceive color as a 3 dimensional space; and the role of the primary colors is to pick a point in this space by selectively stimulating or masking the 3 response curves. In a world of pure linear algebra, almost any 3 colors would do, but physical reality limits how ideally we can mix them; and how much light they can emit/mask.
Further, the 3 response curves are overlapping, so there is no set of ideal colors that would let you actually control the 3 curves independently.
[0] At least for color perception in a typical human.
The linear algebra argument for almost any three colors only works if you can have negative intensities. I don't know how to do that with stimulation of photoreceptors, so I don't think that applies here.
Besides having 3 primary kinds of photoreceptors, there are additional complications caused by the initial processing of the color information in the visual system.
Besides the 3 primary color sensations from the red, green & blue receptors, there are a few dedicated detectors for some colors.
Yellow is detected when red is equal to green and both have a high enough brightness. White is detected when red, green & blue are equal and all have a high enough brightness. While black could be detected later, by the lack of information on the other channels, it seems that it also has a dedicated detector.
This gives 6 primary color sensations, where the colors are not perceived as a mixture of colors, like it is the case for orange, blue-green, violet, purple or gray. Presumably these 6 colors correspond to separate outputs of the initial color processing stage of the visual system.
I do not know whether this is true, but I believe that there also exists a dedicated detector for the color brown. While brown is just orange with low brightness, the "brown" sensation is very distinct and very unlike the differences perceived between e.g. dark red and light red, dark green and light green or dark blue and light blue, where the differences are perceived to be only in quantity, not in quality.
A dedicated detector for brown makes sense, because important things in the environment are brown, e.g. the ground is brown in most cases, because it is composed of a mixture of white oxides with red, yellow and black oxides of iron and manganese. Also wood is frequently brown and also many mammals are brown.
Related: some colors can only be perceived by selectively hitting the right cells with tiny lasers.
https://www.scientificamerican.com/article/researchers-disco...
Put this in a VR headset, and maybe they'll finally sell? Ultra HDR
I am surprised that the Purkinje effect and the degree of illumination are not mentioned. For example, should the primary colors be shifted depending on illumination?
https://en.wikipedia.org/wiki/Purkinje_effect
"Artists traditionally" is doing a bit of heavy lifting here. Neither artists nor art teachers explain a concept that all colours can be mixed from RBY primaries for the simple reason that the jig is up the moment they start painting. Rather artists very loosely describe these colours as primaries as a starting point to the concept of mixing colour.
In actual art classes they teach the colour wheel, which usually leads to around 6 colours being used for general painting in addition to white and other colours to darken. They're also not super fixated on what these colours should be specifically instead using terms such as "warm red and cool red", "warm blue and cool blue" etc. There is always a constant recognition that these will still present a limited gamut and that may be a deliberate artistic choice.
There is also an understanding that additional paints may be needed for getting a stronger colour or simply the convenience of not having to mix so much. This thinking continues through into professional printing hence the Pantone system or more interestingly with certain Epson printers that can include ink tanks specifically for violet, green, orange (amongst many others) - where the software will do the heavy lifting of blending these colours with the CMY model to produce a vivid gamut.
On the topic of "Key". Key is the pigment used to introduce detail and tone. For a two colour artwork the Key could simply be the darker of the two shades. We know it as black, but in some print processes it's an imperfect black-like colour that blends well with CMY to produce detail. Again in those Epson printers mentioned earlier, multiple blacks are used depending if it is to be used for creating detail in the coloured areas or simply as a block of black.
This fact blew my mind as an adult…I thought that colors were in fact derived from one another for my whole childhood.
I don’t understand why we can’t teach the color wheel as a true wheel.
But then again I recently said to a friend that “primary colors is just a social construct” and that didn’t go so well…
> I don’t understand why we can’t teach the color wheel as a true wheel.
Is it even a wheel though?
It’s not, it’s a weird loop shape: https://en.wikipedia.org/wiki/CIE_1931_color_space
You can distort this shape into a circle but you lose the geometric relationship between chromaticities—two points an equal distance along the circumference of the color wheel don’t necessarily feel “as different” from each other.
Even this is a simplification. The color space you see is three-dimensional, because that is the physical reality of how your eyes work. Any representation of the color space in two dimensions involves choosing a projection that distorts reality.
Sort of. Your photoreceptors are sensitive to overlapping frequencies, which means they’re not linearly independent and therefore cannot form the basis vectors of a 3D space.
CIE XYZ accounts for this by projecting SML excitations down to a 2D plane (XY) and making the third dimension a color-independent luminosity (Z). Since it’s luminosity-independent, the 2D slice is directly analogous to the color wheel.
Related is that English has 11 basic color terms: black, white, red, green, yellow, blue, brown, orange, pink, purple, and gray. As a result, trying to teach cyan and magenta as primary colors will be much harder than teaching blue and red as primary colors.
For more on basic color terms: https://en.wikipedia.org/wiki/Color_term#Basic_color_terms
You don't think 5-year-olds can learn two new fancy colors?
Those two colors look like blue and pink, so yeah they are gonna confuse them.
Or, they'll think this is obviously not blue, this is cyan.
Eliminating from your 11-item list the words that cannot designate saturated colors, i.e. black, white, brown, pink and gray, there remain 6 words for saturated colors: red, orange, yellow, green, blue and purple.
Besides these 6 words, 2 more words are useful for naming saturated colors. The use of the word "violet" is widespread enough that it should be added to the list as a basic English color term.
The distinction between violet and purple is that while both are mixtures of red and blue, violet contains a small enough amount of red that it can be matched by a monochromatic color in the violet range of the spectrum, while purple contains an amount of red that is great enough so that it can be matched only by a mixture of monochromatic red with monochromatic blue.
A word is needed for the blue-green color. Cyan is a misnomer that should be avoided, but "turquoise" is a word that has been used in English for many centuries for designating the blue-green color (and which is used for the same purpose in many other European languages, all of which have borrowed the word from French, like also English). "Teal" is another synonym for "blue-green", which has been introduced in the 20th century.
There have been many misunderstandings about the words used by Isaac Newton for his circle of colors, but I believe that when his words are interpreted correctly, he was right.
Isaac Newton has divided the saturated colors into 8 colors: red, orange, yellow, green, blew or blue, indico or indigo, violet and purple. The first 7 of these were classified as prismatic colors, i.e. as monochromatic colors.
Isaac Newton spelled blue as both "blew" and "blue", and also indigo was spelled as both "indico" and "indigo". While the meaning of the other color words is not ambiguous, the meaning of these 2 words is not clear.
The words used by Isaac Newton were the names of some paints, whose hue he compared with the colors obtained by the dispersion of the solar light. The "indico" paint was presumably made with the indigo pigment, so it must have been blue.
The "blew" or "blue" of Isaac Newton was the color of the "blue Bise" paint. "Bise" is more frequently spelled "bice" and it was the name of a paint based on copper carbonate. Depending on the exact details of its method of preparation, such a paint will contain a mixture of malachite and azurite pigments, so it might have any hue between green and blue. We do not know who was Newton's paint supplier or any other details about the paint used by Newton, so it cannot be known for sure which was the real color of Newton's "blew".
Nevertheless I assume that Newton's "blue Bise" was actually a blue-green paint, because only in this case Newton's classification of the saturated colors will make perfect sense, because blue-green and blue are distinctive enough to deserve to have their own names.
So translated into modern English, the 8 saturated colors of Isaac Newton would be: red, orange, yellow, green, turquoise, blue, violet and purple. This classification remains right.
While you are right, "magenta" is just a fancy synonym for "purple". It might have been chosen instead of "purple" because the traditional word could be applied to colors having various proportions of red and blue, while "magenta" is intended to convey that the amounts of red and blue are equal. However all the traditional color names, like "red", "green" or "blue" refer to wide ranges of hues, not to a precise hue, so there was really no good reason for the use of the word "magenta".
"Cyan" is a very bad word choice caused by confusions in the translations of Ancient Greek texts made by philologists ignorant of chemistry and mineralogy. In Ancient Greek, "cyan" meant pure blue, not blue-green. More precisely, it was the color of the ultramarine blue pigment, the most expensive blue pigment at that time, which was imported from the present territory of Afghanistan and for which the name "ku-wa-no" was already used by the Hittites, a millennium before the Greeks. Nowadays ultramarine blue is still used as a pigment, but it is made synthetically, so its cost is a small fraction of what it was before the 19th century.
Before the use of "cyan" has started, the color name "blue-green" had been used for a very long time. Similarly, "orange" is a relatively new English word, but the color had been mentioned for many centuries, as "red-yellow" or "yellow-red".
So the awareness of distinct hues is not necessarily limited to the set of simple color words, because most languages have used compound words to name the hues for which they did not have a simple word.
Other languages have used the names of well-known colored objects to distinguish the hues that did not have distinct names. For instance, in Latin the word for "red" was used for both red colors and purple colors. When Latin speakers wanted to specify whether something was red or purple, they would say "red like the kermes (red) dye" or "red like the purple dye" (the word "purple" as a color name comes from the latter expression). Similarly, in Latin the word for green meant either green or blue-green. To distinguish the 2 colors, a Latin speaker would say "green like grass" or "green like leaves" or "green like emeralds" for expressing "green" and "green like the littoral sea" or "green like beryls" or "green like turquoise gems" for expressing "blue-green". So they were well aware about the differences between these colors, even if they did not have distinct words for them.
You have it backwards. Purple is a fancy synonym for dark magenta.
Purple is attested as a color name in English for about 600 years.
Before that, it has been used as a color name in various languages that have borrowed it from Latin or directly from Greek, where it had been used for about 3000 years or more.
Magenta has been used as a color name in English since 1860, "named in honor of the Battle of Magenta in Italy, where the French and Sardinians defeated the Austrians in 1859".
Initially, magenta was not a generic color name, like today, but it designated a certain cheap aniline dye, of purple color.
So purple cannot be considered a synonym for the neologism "magenta". Magenta could be considered as a certain specific shade of purple, except that during the time it has been applied to different dyes, depending on the evolution of dye technology, so the word "magenta" has not meant always the same color, but at most a range of purple colors that was never defined precisely.
[dead]
One of the things I love about “Contact” is that the contact mechanism chosen by the aliens was so close to what I guessed aliens would use when I first learned about SETI.
Decimal is not universal. Not seconds, not meters, not sound frequencies used for communication, not colors. Our sky isn’t blue, it’s purple. Ask any bee and they’ll tell you. But hydrogen glows at very specific colors and that only changes if you are moving fast enough.
The fundamental colors are the colors of the elements and, I might argue, their oxides. As reflected by light or when they incandesce. Gold. Rust. Arsenic green. Carbon black. Maybe the emission bands of noble gases, though those are hardly every day items.
(If I were a very clever alien though, and I discovered exotic states of matter where the elements behaved differently, and I only wanted to talk to other very clever aliens, I might use those instead to talk over the heads of the younger or dumber species, which is why I stopped contributing to SETI. We are looking under the wrong rocks, IMO).
The Aurora colors are similarly universal.
The most common green color from excited nitrogen molecules going back to normal by emitting 557.7 nanometer photons. Oxygen makes 650 nm red, and the 427.8 nm blue is from nitrogen ions.
So with human cones at 564–580 nm, 534–545 nm, and 420–440 nm, seems like we could do with one cone being redesigned.
You may recognize the author of this blog, he created and illustrated the Dinotopia series of books in the 90s.
https://en.wikipedia.org/wiki/Dinotopia
I loved those books when I was a kid
It is easier to understand additive primaries through a chromaticity diagram. You can form colors by mixing the primaries, and the gamut is determined by the hull of the primaries. Obviously you need at least three of them to enclose a space.
https://commons.wikimedia.org/wiki/File:CIE1931xy_gamut_comp...
There’s more to colour perception than the cone cells in the retina. There’s also the opponent process in the visual cortex, which is where preschool primary colours come from. https://en.wikipedia.org/wiki/Opponent_process
As somebody living in central europe I have never in my life met somebody who claimed that yellow is a primary color. The fact that this could be a thing puzzles me beyond believe.
Gourney Color and Light and one of the same name by Pickard et al. are a really good artist centric exploration of color.
FWIW, I thought the human eye is wired for Red Yellow Green Blue
Blue and red