Color Questions & Misperceptions
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We use our brains to perceive colors, but colors themselves exist in the external world (outside our brains), because light wavelengths have colors don't they?
No.
It is certainly true that, either from ignorance or simply for convenience, people typically speak as if colors are innate properties of objects, not something created in the mind, and this is how we intuitively understand the world. But when we stop to consider what we now know about how color works, it is just as plain that while the illusion is one of extrinsic properties, when people are talking about color they are indeed talking about a function of the brain, not anything that exists outside of their heads.
Some people may say they are actually referring to certain wavelengths of light from the extrinsic world (though again, they are not typically conscious of the mechanics). But a few thought experiments will show that this correlation is not what we typically understood when we learned that "the leaves are green because they reflect green light." What we typically mean by color is not (whether we realize it or not) any property of light waves or anything that actually exists outside of the mind.
"Consider, for example, the six "primaries" red, green, yellow, blue, black and white and the phenomenal structure that color exhibits in virtue of their relations. There is nothing in the light waves themselves that accounts for this sixfold structure: the spectrum is rather a physical continuum." (CV p64)
Indeed, the very idea of "primary" colors indicates something that is entirely apart from the extrinsic world (extrinsic to the human mind, that is). There are no "primary" wavelengths. The distinctions in how certain colors combine while others do not has no parallel in the continua of light wavelengths.
Think of all the rules and knowledge we have built around color -- for example, that mixing the color red with the color blue creates a third color we call "purple." Whether people recognize it or not, these are references to rules that apply strictly within the brain, not any reality that exists outside the brain. Adding light wavelengths of 480nm (which appear blue in the spectrum) to wavelengths of 650nm (which appear red in the spectrum) does not create any new wavelength. It certainly does not create light rays of wavelength 430nm (which appear purple in the spectrum). When you mix red paint with blue paint the resulting paint only reflects wavelengths that the two colors reflected previously when they were separate. All the things we know about mixing colors and which colors can be formed from other colors, etc. etc. has absolutely no meaning in strict terms of light wavelengths.
Here is another example: Consider the bars A, B, and C below:
Are bars A and B more similar in color than bars B and C? People would commonly say that they are. But if so, they are certainly not talking about anything that exists outside the mind, for in no way is A more similar to B in the extrinsic world of nature. Bars A and C are taken from points equidistant from B in the light spectrum continua:
Thus if one would typically say that A is more like B in "color," they are not talking typically about any "color" or any other quantity that is not created in the mind.
Yes, for most humans, the exact same light information will produce the same color experience, and yes this is information about the outside world correlating to perceptions in the brain. But just as a sharp knife poking our hand in the extrinsic world consistently correlates to pain, that does not mean that the pain itself exists outside our brains.
Thus if other animals map different colors to the same light information -- as we know they do -- their colors are no less correct or real than our colors. Similarly, if extraterrestrials evolved color vision, we could be confident neither their color perceptions nor their hue boundaries would be the same as ours because that would be a fantastical coincidence for a species that didn't share our genetic history. Similarly, if the alien brains mapped sound sensations to light information and color sensations to compressed air, this would be no less valid a mapping of objective reality than ours. (Indeed, some human "synesthetes" have experiences similar to this.)
Do we see the same colors? Could we ever know?
This is the question that started my hunting down color perception and cognitive science texts. It turned out to be surprisingly hard to find the answer.
Suppose that you were born with a brain that sees the color blue where others see the color red. Firetrucks or blood oozing from a wound always looked blue to you. Of course no one can see inside your mind, nor you into others, so you would simply learn that "red" is the name of that color you see when you look at a firetruck. You would probably go through life never having a clue that you were actually perceiving very different colors when you and another person looked at the same object.
Further, we have no idea how or why the mind chose certain colors to represent particular ranges of perceptions of the outside world. There is nothing logical or inevitable about the brain mapping red perceptions to one particular set of stimuli and green to another, rather than vice versa. It was a basically random association at some point -- how do we know it isn't rather randomly matching them differently in each of us as we are conceived?
So given this limited binding between the colors we perceive the words we use to talk about them, is there anything scientists could ever do -- now or in the future -- to convince we are actually perceiving the same colors? As it turns out, they can.
Take another look at the visible spectrum:
The brain does not match one color perception to one wavelength. (Indeed, there really is no such thing as a "single" wavelength, but rather a continuum with a nearly infinite variations within variations, upon which we oppose an arbitrary granularity and measurement system and decide to refer to ranges within those units as if they could not be further decomposed.) Not only is it arbitrary which particular colors the brain maps to various portions of the visible spectrum, but it's also quite arbitrary where wavelengths start to change from one major color to another. Thus the "greenish" colors map to a wider spectrum of wavelengths than the "yellowish" perceptions, and the "Blueish" colors map to a wider spectrum than green.
There is nothing magic or special about the particular point in the spectrum where one major hue starts and stops, and it is these "hue boundaries" that convince us that we humans are perceiving the same colors. For since there is nothing specific in the wavelengths where one hue ends and another begins, there is no conceivable reason why varying mappings of colors to wavelengths would draw the hue boundaries in nearly the exact places -- and we know that in typical humans, they do.
Using the same sort of testing we can conclude that many other animals must see very different colors. For example, scientists established theoretically that certain animals like pigeons and turtles must see very different colors from humans because they have a tetrachromatic vision system, as opposed to the trichromatic system of humans. Thus where we envision certain colors combining in terms of 3 "primary" colors, these animals see combinations in 4 color dimensions, and must see combinations of colors that we cannot even imagine.
That pigeons see different perceive objects as different colors than humans was confirmed experimentally by training pigeons to react to hues, and observing where they perceived hue boundaries in the spectrum. For example, pigeons treat wavelengths to either side of 540nm as falling into different hue categories, whereas humans do not.
Do our brains just match a given wavelength of light to a given color perception?
No.
Some people envision color perception as a sort of spectrometer, simply matching N wavelength light to M color perception. But such a mechanism would not be very useful. Scientists believe that color perception evolved to help with tasks such as identifying fruit against a leafy background, distinguishing ripe fruit from unripe, and spotting a potential predator hiding in the grass. But the light wavelengths reaching those objects from the sun and reflected by them to our eyes varies widely hour to hour and day to day with variations in the atmosphere and time of day (e.g. the angle the sun is taking through the atmosphere). Color perception would not be very useful, and probably would have never evolved if, for example, the color of a ripe apple mapped to an unpredictable farrago of color perceptions. Thus the brain takes in light information outside of the apple and continually adjusts color mapping to make the apple keep appearing red, a process called "color constancy."
"Think for a moment what would happen if, on a sunny day, you took an apple out of the bright light of an open field and viewed it in the shade of a low, leafy tree. In the shade, the ambient light would look somewhat green, and yet the apple would continue to look red. Or to take another example, if you placed a white piece of paper in the shade and a black sheet of paper in the sunlight, the black sheet would continue to look black, even though it would now be reflecting considerably more light than the white sheet. In each of these situations, the spectral power distribution of the light reaching the eyes changes dramatically, and yet the colours we preceive are relatively constant. This phenomenon is known as approximate color constancy. (Evan Thompson, Color Vision)
Do Primary Colors Exist?
No.
Handprint.com does an excellent job of summarizing the history and science of this, and I'll quote liberally from them (all quoted portions below).
The myth of primary colors remains strong to this day, and typically takes the following form: "(1) the three primary colors are red, yellow and blue, (2) the primaries exist as three material substances (often identified with specific pigments), (3) the primaries cannot be mixed from other colors, but can mix all other colors."
But the truth is that these three primaries *cannot* mix all other colors. Neither can other popular sets of primaries, such as the CMYK theme of printers.
'... primary colors are either imaginary sensations you cannot see — and "colors you can't see" aren't really colors — or they are actual lights or paints that cannot mix all possible colors, which means they aren't really "primary".'
"What makes these tradeoffs feasible — and often unnoticeable in practice — is the remarkable ability of our color vision to accept different color images as equivalent or identical, provided the gamuts used to reproduce the images retain the relative relationships between all the colors in the image, especially relative lightness and hue. Thus, we can happily watch a Discovery Channel documentary on tropical birds, coastal reefs or erupting volcanos without noticing that the leafy greens, littoral cyans and magma reds are really much duller than they appear in life."
"The reason we don't notice the color difference is that color vision treats all colors as arbitrary, in the sense that the accuracy of a color choice depends on the image context, viewing situation and viewer expectations. Video technology reproduces acceptable color relationships in context, so the image as a whole appears accurate even though separate image colors do not match the actual colors of the represented objects."
Because humans did not understand the overlapping of photocell receptors before relatively recently, various other misconceptions arose among artists of past centuries, are are still widely believed today:
'The first misconception is that "primary" colors must be visible colors, in the sense that an artist can pick a color of sticky paint or a wavelength of visible light and say, "there, that is the primary yellow". But ... it is no more possible to find a paint that looks like "primary" yellow than it is to find a dog that looks like Cerberus.
The mind never has direct experience of the "primary" signals from our three photoreceptors. The essential difference is not between one shade of color and another but between a visible color and an imaginary color.'
'The second misconception is that "primary" colors must be specific colors, in the sense that an artist can pick one color of primary yellow paint as the "nearest match" to the "true" primary yellow color, or that one primary yellow paint is the "best" primary yellow. ... But, as we have seen, the selection of real colorants is always arbitrary ... Almost any three colors can serve as primary colors, depending on how you want to use them.'
'The third misconception is that none of the various colors of primary paints are the "true" primary color because all paint colors are "impure" or polluted by added light from the other two primaries. ... This is an especially quaint anachronism from the 18th century, and it is wrong from several points of view. If a paint really were "pure" and only reflected a single wavelength of light (which is the "purest" possible color stimulus), the paint would have a luminance factor near zero and would appear blacker than the "purest" black paint! And that monochromatic "yellow" light is no more saturated than a mixture of a monochromatic "orange" and "yellow green" light, so light purity is not the cause of hue purity. Finally, even if our primaries were three "pure" colors of light (regardless of their hue), we still couldn't mix all other colors. "Purity" or pollution has absolutely nothing to do with the limitations of primary colors of paints or dyes.'
'All three misconceptions are forms reification — the belief that primary colors are real.... Are "primary" colors actually memory colors? Are they specific colorants? Are they produced by subtractive mixture, or additive perception? Are they cone outputs, or opponent codes? Specificity evaporates the concept, in the same way that specificity evaporates the concept of "beautiful".'
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'The first primary paradox is: Primary colors are either imaginary, invisible "lights" that can describe all colors, or they are imperfect, real colorants that reproduce only some colors.
This double impossibility — you can't mix all colors with the primary colors you can see, and you can't see the primary colors that can mix all colors — arises from the physiology of color vision, the way the human eye is structured.
The sensitivity curves of the L, M and S cones overlap each other: every monochromatic (single wavelength) hue must stimulate two or even three cones simultaneously. As a result, the boundary of visible colors curves away from the "pure" primary corners of a mixing triangle, creating the horseshoe shaped chromaticity space of visible colors (right).
Because of its curved borders, the chromaticity space cannot be completely enclosed by any triangle defined by three monochromatic lights RGB around its border, and therefore all visible primaries cannot mix all possible colors — which makes them imperfect. Any three primary colors XYZ that completely enclose the chromaticity space, and therefore define all visible colors, must located outside the chromaticity space of real colors — which makes them imaginary.'
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' The second primary paradox is: All choices of imaginary primary colors are arbitrary; they are only measurement units. All choices of "real" primary colors are arbitrary; colorant selections depend on cost, availability, convenience, medium and image quality.
The imaginary primaries used in colorimetry are simply standardized units of measurement, like the meter, joule or yen. Just as the imaginary foot used in distance measurement does not represent a real human foot, the imaginary primaries used in color measurement do not represent real lights. Just as the meter could be longer or shorter and still work just fine as a standard unit of measurement, there is an infinite number of triangles of different sizes or shapes that would completely enclose the chromaticity diagram (right) and therefore would work just fine as a standard color gamut of imaginary primaries.
As with most measurement units, the imaginary XYZ primaries have been adopted in part for reasons of convenience. The transformation matrix used to define the imaginary primaries was chosen to reproduce the luminous efficiency function in the Y primary, but this was an arbitrary decision. All imaginary primary colors are arbitrary.'
CMYK
'Pigment innovation has even created entirely new primaries and new systems of color mixing. Thus, magenta was not identified as a subtractive primary color until the CMYK system was invented by Alexander Murray in 1934, because suitably lightfast magenta inks were unavailable before then. The CMYK system, in turn, cannot reproduce many saturated oranges, violets, blues and yellow greens, and in specific applications where brighter colors are required, newer printing systems with larger gamuts — Hexachrome™ (six primary colors of ink) or Heptatone™ (seven primary colors) — can be used instead.'
Is black the lack of color and white the combination of all colors?
No.
Newton himself recognized this. Newton 'concluded that spectral "orange" or "violet" light is just as primitive or basic as "red" or "yellow" light, because none of these spectral hues can be broken down into a more basic color. However, they can be mixed in any combination to make all the colors of nature, including white and black and colors (such as magenta) not found in the spectrum.'
Newton found: "White is not the acme of all color phenomena but a murky mixture, no purer than dust or dirt, that can be produced in many different ways. All these ideas went against the grain of Aristotelian theory and well beyond the dyer's lore that three 'primary' colors defined color mixing." (MacEvoy, http://handprint.com/HP/WCL/color2.html)
The visual impression experienced in directions from which no visible light reaches the eye is black. But there are several problems with simplistic views of black and white implied in the question. For example:
- White can be formed by only two (antagonistic) colors
- White light does not contain purple (isn't purple a color?)
- Other colors, e.g. red, are seen as black in certain contexts
- if you are looking at a piece of black paper and a piece of white paper in the shade of a tree, then take the pieces out into the bright sun, the black piece will still look black even though it is reflecting **much** more light than the white piece was in the shade.
Technically, white is the impression of any combination of colors of light that equally stimulates all three types of color-sensitive visual receptors.) Pigments that absorb light rather than reflect it back to the eye "look black". A black pigment can, however, result from a combination of several pigments that collectively absorb all colors. If appropriate proportions of three primary pigments are mixed, the result reflects so little light as to be called "black".
"White and black are also colors (in particular, black is not the absence of color but a distinct color experience), and their perception is closely related to the amount of light or luminance in the visual environment." (Bruce MacEvoy, http://handprint.com/HP/WCL/color1.html)
"What an organism perceives as "white light" is actually a combination of all wavelengths that that organism is sensitive to. For humans, that basically corresponds to combinations of the three wavelengths of light we are most sensitive to. Goldfish, however, besides having red, green, and blue pigments like humans (or long-, medium, and short-wave sensitive pigments) have an additional pigment that responds in the ultraviolet range. From a previous round of behavioral tests, Neumeyer was able to determine a mixture of primaries that would stimulate appear as white light with a UV component." (Mike Siuta, http://instruct1.cit.cornell.edu/courses/bionb424/students2004/mas262/behavior.htm)
Did the brain evolve to see the world the way it is?
No.
Our senses evolved to maximize survival and reproduction. Even if our brains *could* perceive the world accurately (increasingly dubious as physicists move toward a reality of many hundreds of dimensions and a more descriptive model than space-time), our brains would be besieged with data -- e.g. billions of light information enter the eyes each second. To enable faster response time and better survival chances, brains must compress and filter data, and present the best model possible to respond and operate in reality, not to comprehend it, just as the model of our computer desktop, e.g. an icon for a file, allows us to operate much more effectively than perceiving all the individual higher and lower voltages of each bit that comprises the file.
"Our hunch, in short, is that truer perceptions are fitter perceptions. Evolution weeds out untrue perceptions. This is why our perceptions are windows on objective reality. These hunches are wrong." - Donald Hoffman, The Case Against Reality
"The brain did not evolve to see the world the way it is. It can't. Instead the brain evolved to see the world in ways that were useful in the past." Beau Lotto
Also: Reality
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