“What could be simpler or more obvious than colors? The sky is blue. Fresh grass is green. Blood is red. The sun and moon are yellow. We see colors as inhering in things. Blue is in the sky, green in the grass, red in the blood, yellow in the sun. We see color, and yet it is false, as false as another thing we see, the moving sun rising past the edge of the stationary earth. Just as astronomy tells us that the earth moves around the sun, not the sun around a stationary earth,
so cognitive science tells us that colors do not exist in the external world. Given the world, our bodies and brains have evolved to create color. Our experience of color is created by a combination of four factors: wave-lengths of reflected light, lighting conditions, and two aspects of our bodies: (1) the three kinds of color cones in our retinas, which absorb light of long, medium, and short wavelengths, and (2) the complex neural circuitry connected to those cones.Here are some crucial things to bear in mind. One physical property of the surface of an object matters for color: its reflectance, that is, the relative percentages of high-, medium-, and low-frequency light that it reflects. That is a constant. But the actual wavelengths of light reflected by an object are not a constant. Take a banana. The wavelengths of light coming from the banana depend on the nature of the light illuminating it: tungsten or fluorescent, daylight on a sunny or a cloudy day, the light of dawn or dusk. Under different conditions the wavelengths of light coming from the banana will differ considerably, yet the color of the banana will be relatively constant; it will look pretty much the same. Color, then, is not just the perception of wavelength; color constancy depends on the brain’s ability to compensate for variations in the light source.
Moreover, there is not a one-to-one correspondence between reflectance and color; two different reflectances can both be perceived as the same red. Another crucial thing to bear in mind is that light is not colored. Visible light is electromagnetic radiation, like radio waves, vibrating within a certain frequency range. It is not the kind of thing that could be colored.Only when this electromagnetic radiation impinges on our retinas are we able to see. We see a particular color when the surrounding lighting conditions are right, when radiation in a certain range impinges on our retina, and when our color cones absorb the radiation, producing an electrical signal that is appropriately processed by the neural circuitry of our brains. The qualitative experience that this produces in us is what we call “color.” One might suppose that color is an internal representation of the external reality of the reflectance properties of the surface of an object. If this were true then the properties of colors and color categories would be representations of reflectances and categories of reflectances. But it is not true. Color concept have internal structure, with certain colors being “focal.” The category red, for instance, contains central red as well as noncentral, peripheral hues such purplish red, pinkish red, and orangish red. […] Color is not just the internal representation of external reflectance. And it is not a thing or a substance out there in the world.”— George Lakoff and Mark Johnson, Philosophy In The Flesh: The Embodied Mind And Its Challenge To Western Though, P. 23 (via blackestdespondency)