What is Color?

On a simple level, color is first and foremost a personal experience. It is an important part of the total visual and emotional experience we have, for example, when standing at the edge of the Grand Canyon at sunset, or when walking through the galleries of the Uffizi Museum in Florence. We can identify without difficulty with the statement of the philosopher Bertrand Russell: “I know [a] color perfectly and completely when I see it” (Russell 1912). But communication about color is problematic. There is little if anything objective about color experiences, only each individual knows what she or he experiences. Any objective part of color deals entirely with the definition of color stimuli, but, as discussed in more detail in Chapter 4, there is considerable variation in color stimuli perceived as having unique hues, particularly for green and red. There is as yet no indication that selection of such stimuli is tied to variation in specific cone sensitivity of the observers and the presumed resulting subtractive opponent color functions. Color perceptions seem to be generated in detail at a level of brain activity beyond that of the first generation of cone opponent signals.