What is colorblindness?
Many people think a person who is "colorblind" only sees black and white ‹ like watching a black and white movie or television. This is a big misconception and not true. It is extremely rare to be totally colorblind. There are many different types and degrees of colorblindness; rather they are "color deficiencies," since virtually no one is truly blind to all colors.

Colorblindness (color vision deficiency) is a condition in which certain colors cannot be distinguished; it is most commonly due to an inherited condition. Red/Green colorblindness is by far the most common form, about 99%, and causes problems in distinguishing reds and greens. Another color deficiency, Blue/Yellow, also exists, but is rare and there is no commonly available test for it.

Colorblindness is more common in males than females. Approximately 10 million American men ‹ fully 7 percent of the male population ‹ either cannot distinguish red from green, or see red and green different from most people. Colorblindness, however, affects only .4 percent of women. The fact that colorblindness is so much more prevalent among men implies that it is carried on the X chromosome, of which men have only one copy. (Women are protected because they have two X chromosomes; a normal gene on one chromosome can often make up for a defective gene on the other.)

There is no treatment for colorblindness, nor is it usually the cause of any significant disability. However, it can be frustrating for individuals affected by it. Being color blind does keep one from performing certain jobs and makes others difficult. (Distinguishing traffic lights and signs, purchasing clothing and coloring are examples of areas where a person who is colorblind can have difficulty.)

How colorblindness works
Colorblindness is a malfunction of the retina (a neuro-membrane lining the inside back of the eye), which converts light energy into electrical energy that is then transmitted to the brain. Two types of photoreceptor cells in the retina accomplish this conversion: rods and cones.

	The cones are responsible for encoding color. (Rods give us our night vision.) Each cone contains structures or visual pigments sensitive to one of three wavelengths of light: red, green, and blue. Normal persons are able to match all colors of the spectrum by mixtures of only three fundamental color sensitivities. Hence, the huge variety of colors we perceive stems from the cone cells' response to different compositions of wavelengths of light.
	Defects in color vision occur when one of the three cone-cell color-coding structures fails to function properly. One of the visual pigments may be present and functioning abnormally, or it may be absent altogether.
	Colorblindness is normally diagnosed through clinical testing. (The Ishihara color test is the most common test used.) Although there is no treatment for colorblindness, most color-deficient persons compensate well for their defect and may even discover instances in which they can discern details and images that would escape normal-sighted persons. At one time, the U.S. Army found that colorblind persons could spot "camouflage" colors where those with normal color vision are fooled by it.