You also learn to compensate in other ways. For example, even though you can’t distinguish red from green the way most people do, you’ve learned to stop when the light on the top of a traffic light is lit and to go when the bottom light is illuminated.

In fact, most forms of color deficiency are relatively subtle; people are rarely completely color blind, although people often erroneously use the term color blindness for what we have been referring to as color deficiency or color defect. True color blindness is associated with albinism, and a person with this genetic defect lacks an enzyme needed to form the pigment normally found in the skin, hair, and eyes. As a result, the person’s hair is white and his or her eyes and skin are pink. In addition, the vision of a person with albinism is exclusively rod vision. Recall from our discussion of the retina that rod vision is achromatic, or without color. Rod vision also lacks acuity (ability to see details) and is relatively sensitive to light, which tells us that a person with albinism will have rather poor vision for details and will experience normal daytime lighting as excessively bright.