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[berto]

Recall that the human eye is sensitive to the three primary colors of light - red, blue and green - and that this is possible because the eye has one type of cone sensitive to each of these colors. If a person can't see one of these basic colors, then he or she won't be able to see the colors created from combining that color with the other two basic colors. Instead, the person will most likely confuse those shades with others they can see.

Dichromasy, the major type of colorblindness, is a term describing people who have only two of the three major types of cones in their eyes. The three types of dichromasy are:

1.Protanopia    
    
Red blindness - Protanopes cannot see reds, or any color that is a mix of red and the other two primary colors. These shades of red are confused with shades of green or blue. For example:
red    violet    blue
A mix of red and blue (violet) would appear blue to a protanope.    

2. Deuteranopia

Green blindness - Deutanopes cannot see greens, or any color that is a mix of green and the other two primary colors. These shades of green are usually confused with shades of red. For example:
green    white    violet
A mix of green and violet (white) would appear purplish to a deutanope.    

3. Tritanopia

Blue blindness (rare) - Tritanopes cannot see blues, or any color that is a mix of blue and the other two primary colors. These shades of blue are confused with shades of red or green. For example: blue    cyan    green
A mix of blue and green (cyan) would appear greenish to a tritanope.


Both protanopes and deutanopes are considered red-green blind, since they usually confuse reds with greens and vice-versa.

Those who are completely color blind have achromatic vision, meaning they can't see any colors at all. To them, there would be no difference between seeing something in real life and the same image on a black and white television.

Causes:

In almost all cases, color blindness is genetic - an inherited disorder. A boy is much more likely to inherit it than a girl from their parents. This is because color blindness is a sex-linked trait. This means that a boy only needs to inherit one gene from his mother or father to be colorblind, while a girl must inherit two genes - one from her mom and one from her dad - to be color blind. If a girl has only one color blindness gene, then she is considered a carrier. That means that she can pass it on to her children, but she herself does not exhibit color blindness.

Correction:

It is currently not possible to "cure" color blindness. However, special contacts have been developed that help color blind people tell apart certain colors they wouldn't normally be able to distinguish. Also, for example, color blind people could drive since the traffic lights are always in a standard position.

Detection:

A variety of tests are used to detect color blindess and the degree of it. You may be familiar with the tests which require the viewer to identify shapes or numbers in a bunch of colored dots. People with normal vision would see the object, while a color blind person would see a different object, or no distinguishable object at all.