Colorblindness by Rebecca Grant

Five to 8% of the men and 0.5% of the women of the world are born colorblind. That is as high as one out of twelve men and one out of two hundred women. The human eye sees by light stimulating the retina (a neuro-membrane lining the inside back of the eye). The retina consists of Rods and Cones. The rods, located in the peripheral retina, grant us our night vision, but can not distinguish color. The cones, located in the center of the retina (called the macula), operate poorly at night but allow us to perceive color during daylight conditions.

The cones each contain a light sensitive pigment, which is sensitive over a range of wavelengths. Each visible color is a different wavelength from approximately 400 to 700 nm. Genes contain the coding instructions for these pigments, and if the coding instructions are incorrect, the wrong pigments are produced, and the cones are sensitive to varied wavelengths of light, resulting in a color deficiency. The colors people see are completely dependent on the sensitivity ranges of these pigments.

There are many of misconceptions about colorblindness. The idea is anyone labeled as "colorblind" only sees black and white – comparable to watching a black and white movie or television.
It is extremely rare to have monochromasy - complete absence of any color sensation or, totally color blind.

There are many different types and degrees of colorblindness or more correctly called - color deficiencies.

  People with Trichromasy vision have normal cones and light sensitive pigment. These people are able to see the numerous different colors and subtle mixtures of them by using the cones sensitive to one of three wavelengths of light - red, green, and blue. A mild color deficiency is present when one or more of the three cone's light sensitive pigments are not right and their peak sensitivity is shifted. These deficiencies include protanomaly and deuteranomaly. A more severe color deficiency is present when one or more of the cone’s light sensitive pigments is severely shifted. These include protanopia and deuteranopia.
  Protanomaly occurs in one out of 100 males. Protanomaly is referred to as "red-weakness." Any red colors or shades seen by a normal observer appears more weakly by the protanomalous viewer, both in terms of its saturation, or depth of color, and its brightness. Red, orange, yellow, yellow-green, and green appear shifted in hue towards green, and all appear paler than they do to the normal observer. The red component that a normal observer sees in a violet or lavender color is so weakened for the protanomalous observer that he may fail to detect it, and therefore sees only the blue component. Hence, to him the color that normal people call "violet" may look like just another shade of blue. Under poor viewing conditions, such as driving in bright sunlight or in rainy or foggy weather, it is easily possible for protanomalous individuals to mistake a blinking red traffic light for a blinking yellow or amber one. In addition, these individuals may also fail to distinguish a green traffic light from the various "white" lights in storefronts, signs, and streetlights.

Deuteranomaly affects five out of 100 males. The deuteranomalous person is considered "green weak". Similar to the protanomalous person, he is poor at discriminating the small differences of hues in the red, orange, yellow, and green region of the spectrum. He makes errors in the naming of hues in this region because they appear shifted towards red for him. Deuteranomalous individuals do not have the loss of brightness problem faced by many protanomalous persons. From a practical stand point though, many protanomalous and deuteranomalous people breeze through life with very little difficulty doing tasks that require normal color vision. Some may not even be aware that their color perception is in any way different from normal.

Dichromasy affects two out of 100 males and can be divided into protanopia and deuteranopia. These individuals normally know they have a color vision problem and it can effect their lives on a daily basis. They see no perceptual difference between red, orange, yellow, and green. All the colors that seem so different to the normal viewer appear to be the same color for this two percent of the population.   Protanopia occurs in one out of 100 males. For the protanope man, the brightness of red, orange, and yellow is more reduced compared to normal. This difference can be so pronounced that reds may be confused with black or dark gray, and red traffic lights may appear to be extinguished. These men may learn to distinguish reds from yellows and greens primarily based on the apparent brightness or lightness, not on any perceptible hue difference. Violet, lavender, and purple are indistinguishable from various shades of blue because their reddish components appear so dimmed they are invisible, e.g. Pink flowers, reflecting both red light and blue light, may appear just blue to the protanope.   Deuteranopia affects one out of 100 males. The deuteranope suffers the same hue discrimination problems as the protanope, but without the abnormal dimming. The names red, orange, yellow, and green really mean very little to him aside from being different names that every one else around him seems to be able to agree on. Similarly, violet, lavender, purple, and blue, seem to be too many names to use logically for hues that all look alike to him.


It should be obvious there are several different kinds and degrees of color vision deficiencies. Protanomalous or deuteranomalous individuals can usually pass as a normal observer in everyday activities. They may make occasional errors in color names, or may encounter difficulties in discriminating small differences in colors,
but usually they do not perform very differently from the normal except on color vision tests.

The protanope and deuteranope, on the other hand, can be severely color deficient. The real problem, as a protanope or deuteranope may see it, is there are far too many hue names used by most people without any obvious basis for using one instead of another. Why call something "orange" when it does not look different in any way from something else called green, tan, beige, or any of several other color names?

It is important to get children’s vision tested at an early age. Here are some examples of colorblind tests given at a doctor’s office:

  number 5 in color test
  number 10 color disguised  
number 9 in color perception test   numeral 3 within color dots - links to next project