In this chapter we noted how ideas about color vision have developed over the past 300 years. In answer to the question "What is color," we emphasized that a complete answer must take into account multiple factors: the pigmentation of the surfaces of the objects we're looking at; the wavelength composition of the light illuminating those surfaces; the presence of appropriate photoreceptors in the eye for analyzing that wavelength composition (our eyes have three spectrally broad and widely overlapping cone photopigments); and brain mechanisms able to estimate surface color based on the outputs of those photoreceptors (mechanisms that include chromatic and achromatic visual channels). We also stressed that color depends on context and on the adaptation state of the visual system.

Science's success in explaining how people see color also needs to take into account why they see color. Probably, the ability to perceive color developed to help creatures detect and discriminate objects in their environment. Because objects—artificial as well as natural—have characteristic pigments, they absorb and reflect light in characteristic ways. These patterns of spectral reflection make it advantageous to have color vision. An animal whose visual system retains information about the wavelength distribution of reflected light can more easily pick out objects from their backgrounds. Moreover, the colors of the surfaces of objects enable the animal to recognize what sort of objects it has encountered and what kinds of actions those objects call for. Color, in other words, is intimately related to the problem of object recognition. In the next chapter we introduce the three-dimensional quality to vision, a quality that defines the presence, location and shapes of objects.