Color blindness is most often a genetic visual deficiency that limits the colors that an individual can detect. Most people with this condition don't only see in black and white. The colors affected are usually limited to green and red, which often appear as shades of tan or brown. Less often, the color blue may also be affected.
The human eye detects color with photoreceptors located on the retina at the back of the eye. These photoreceptors come in two types, rods and cones. Rods fill the peripheral edges of the retina and are used in low-light conditions, such as in night vision. Rods do not detect color well, but allow people to see in the dark.
Cones appear throughout the retina and contain pigments that are responsive to certain colors. The pigments communicate with the brain when fired. This is how a person detects color. Cones require brighter light to function than do rods, which is why we cannot see colors well in the dark.
Color blindness is a result of certain cones misinterpreting the wavelengths that correspond to their respective colors. Red, green and blue colors have corresponding wavelengths. Red wavelengths are longest, green colors generate medium wavelengths, and blue colors are made of shorter wavelengths. If the green cones, for example, only respond to slightly longer wavelengths, green will be interpreted by the brain as red.
There is no cure for color blindness, but it is usually not an inhibiting condition. Red and green traffic lights might appear to be similar shades of the same color, but those who are color blind use the light’s position as an indicator of when to stop or go. Color blindness becomes more of an issue if work demands color separation. This might be the case for an artist or a designer, for example, or for an electrician who must see red, green and yellow wiring schemes.
Studies suggest about eight percent of the world’s male population is genetically color blind, while less than one percent of the female population is affected. In addition to genetic inheritance, certain diseases or damage to the eyes can cause color blindness. As people age, sensitivity to colors may diminish due to macular degeneration, cataracts or other conditions.