Red-green color-blind people may miss out on the subtle tones of a forest or a bouquet of roses, but they do get compensation. Biologists at Cambridge University and the University of Newcastle upon Tyne in England find that color-blind men are extraordinary connoisseurs of khaki.
Red-green color blindness is caused by an unusual form of a light receptor in the eye, which is sensitive to a different range of colors than normal. This variant type of receptor makes it harder to distinguish among red, orange, yellow, and green. The resulting shift in color perception bestows extra sensitivity to other hues, however, as the researchers demonstrated by asking subjects to rate the similarity of 15 circles painted in tones of khaki. People with regular vision struggled with the test, while color-blind men aced it. The findings lend credence to the theory that people with red-green color blindness make good hunters or soldiers because they are not easily fooled by camouflage. The researchers hypothesize that the variant form of receptor could be an evolutionary relic from the time when early humans needed to spot predators or food hidden in branches and leaves.