Learn about Color Blindness

Are you color blind? Color blindness occurs when a single type of color receptor cone is missing from the retina due to a genetic defect rendering the person unable to distinguish some colors from others. There are three main types of color blindness—green, red and rarely blue.

In this test card both the fork and spade can be seen by people with normal color vision. The spade is purple, a color which is received by the receptor for blue-green in the retina. Since green blind people have no green receptor cones, they cannot distinguish the spade from the background. Similarly, red blind people have no red receptor cones and so fail to see the fork which is red and should therefore stimulate the cones which receive red.

Using a series of such cards, the nature of color blindness can be determined. What do you see?


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