1 How Do Things Look to the Color-blind?

Our question is, how do things look to the color-blind? But what does that mean? Who are the “color-blind”? Approximately 7 percent of males and fewer than 1 percent of females (of European descent) have some form of inherited defect of color vision and as a result are unable to discriminate some colored stimuli that most of us can tell apart. (Color defective is an alternative term that is often used; we will continue to speak with the vulgar.) Color-vision defects constitute a spectrum of disorders with varying degrees and types of departure from normal human color vision. One form of color-vision defect is dichromacy: by mixing together only two lights, the dichromat can match any light, unlike normal trichromatic humans, who need to mix three. The most common form of dichromacy (afflicting about 2 percent of males) is red-green color blindness, or red-green dichromacy, which itself comes in two varieties. A redgreen dichromat will not be able to distinguish some pairs of stimuli that respectively appear red and green to those with normal color vision. For simplicity, we will concentrate almost exclusively on red-green color blindness. In a philosophical context, our question is liable to be taken in two ways. First, it can be straightforwardly taken as a question about visible properties of external objects, like tomatoes. Do tomatoes look colored to dichromats? If so, what color? Second, it may be interpreted as the more elusive—although closely related—question of “what it’s like” to be color-blind. Forget about tomatoes—what is a dichromat’s experience like? This chapter addresses the first question and, for reasons of space, does not explicitly address the second. Put another (arguably equivalent) way, we are asking what colors are represented by a dichromat’s experience. Having now identified the “color-blind,” and the straightforward way in which our question should be taken, a further point of clarification might be helpful. Imagine a bright blue car parked in an underground garage illuminated by orange lighting. Bright blue objects under this lighting look quite distinctive. Those accustomed to the garage