Color blindness, or color vision deficiency, is an eye condition in which the afflicted person cannot see the difference between colors. It does not necessarily refer only to an individual who is entirely color blind, which is someone who only sees in black and white. Different types of color blindness can be found in humans. Along with total color blindness, two other types of the condition are red and green color blindness and blue and yellow color blindness. An individual with certain types of color blindness might have either a partial or total blindness to that color.
To understand the different types of color blindness, it is probably best to first be aware of what makes color vision possible. Put simply, the retina, the part of the eye that allows humans to see, has rods and cones. Rods enable night vision and cones enable color vision. Each cone has a light-sensitive pigment that reacts to the colors red, green or blue. Color blindness is caused by any deficiencies in these pigments.
An individual with regular vision, also called trichromacy, has no pigment deficiencies and is, thus, able to see red, green and blue. Someone with a misaligned pigment has anomalous trichomacy, which means he can see all three colors, but one of the colors looks weaker than it would to a person with regular vision. Dichromacy is when an individual can only see two of the three colors, usually because of a missing or severe problem with the associated pigment. Last, a person who sees only one color is said to have monochromacy.
Within anomalous trichromacy, dichromacy and monochromacy, there are names for each color deficiency. Not being able to see red, green or blue in its full depth and brightness is called protanomaly, deuteranomaly and tritanomaly, respectively. In the same vein, not being able to see red, green or blue at all is called protanopia, deuteranopia and tritanopia. For monochromacy, seeing no colors at all is called typical monochromacy while seeing very little color is called atypical monochromacy.
The colors red, blue and green can be mixed to make up new colors such as the color purple. Since this is so, not being able to see the true extent of a color, or a color at all, affects the way an individual sees the world. For example, a person with protanomaly would see a weakened version of red within a purple object, so to him, that object would appear more blue than purple. Of the different types of color blindness, red and green color blindness is the most common. Blue and yellow color blindness is rare, and total blindness is even rarer.
Though a person with color blindness is generally able to live a normal life, having the condition can hold him back in some areas, such as in obtaining certain jobs. Usually, color blindness is hereditary and, therefore, the affected person does not know the world to be any different. Sometimes, the condition can be caused by other things such as illness and aging. Color blindness is usually diagnosed through the Ishihara Color Test.