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Color blindness is defined as the "inability to see certain colors in the usual way." It is not the "swapping" of colors
such as green and red. Instead, colors appear with the absence of a particular retina cone, causing colors to be more green,
red, or blue, depending on the type of color blindness. To see how how different types of color blindness affect how different
colors are seen, look at the picture to the right.
Protanopia
Often known as red-green color blindness, this is the most common type. It occurs when the long wavelength cones are either
defective or missing. If they are defective, the person is called an anomalous trichromat, because they still have three cones
in their eye, but one isn't working. If one is missing, the person is called a dichromat, because they only have two cones
instead of the normal three.
If you compare the two visions of the normal person and the red-green color blind person (as shown on the right), you can
see that the color blind person not only has difficulty distinguishing between red and green but many other colors as well.
This leads to a wrong idea of red-green color blindness.
Deuteranopia
This is the most common subtype of red-green color blindness, and it is found in about 6% of the population. As with protanopia,
there is much difficulty in distinguishing many hues of color. In addition, there are also two different types. Dichromats,
where the medium wavelength cones are missing, and anomalous trichromats, where the medium wavelength cone is defective.
Tritanopia
This rare type of color blindness is often known as blue-yellow color blindness. However, as before, this term is misleading.
Instead, they mix up blue and green, and yellow and violet. This is caused by the defective or missing short wavelength cone.
Unlike other forms of colorblindness, the gene for tritanopia is not sex linked, making the condition equal between men and
women.
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