Discovering and Developing Talents
© 2002 Stephen Holland
|1 - Explaining Color Deficiency
2 - Traditional Tests
3 - Holland's Online Tests
4 - Percent Test
5 - Brown Test - Results
6 - Color Pencils- Results
7 - Art Test
8 - Thread Test for Children
|1. Explaining Color Deficiency|
|Normal RGB Vision
The human retina has cone cells which see mainly red, green and blue. Other colors are interpreted as mixtures of these. If the red and green cones are triggered, then the brain thinks "yellow".
Computer monitors and TV sets are designed to match human vision. They only have the 3 colors of dots: Red, Green, and Blue. To make yellow, both the red and green dots must be turned on equally. Other colors are variations.
An excellent chart showing computer RGB values for 256 colors.
|What color deficient people see
The following colors are only approximate, because human color sensitivity is complex, but gets across the general idea. I simply took the basic rose picture, and with image editor software reduced red or green.
|Blue deficiency is rare because the numerous rods in the retina
are blue-sensitive, and may fill in the gap
if blue cones are missing.
Total color deficiency is also fairly rare. The normal rose on left would be seen as some variation of gray.
Apparently many common animals, from dogs to cattle, see mostly gray. (A bull does not chase red, but instead chases the motion of a moving cloth or person.)
On the other hand, most birds seem to see color well, or they wouldn't have such glorious feather colors! Bees can see ultraviolet.
(See a scientific discussion of color deficiency genetic aspects at Howard Hughes Medical Institute )
Boys vs Girls
Color deficiency is rare in girls
The genes for color vision are on the X chromosome, and because females have 2 X chromosomes, if one is deficient, the other makes up for it. They even may have more color sensation than males, which might explain why my wife notices color mismatches in my clothing much more than I do. The result is that there are only about 1 in 200+ girls who have color deficiencies, or roughly only one girl in 16 classrooms
Color deficiency is common in boys
Different books give different figures, from 5-8 % of boys, 1 boy in about 12-20, or an average of one boy per classroom has some color deficiency, almost similar to the percentage of people who are left-handed!
More common in Europeans?
It is inherited naturally through the mother, who may pass on a defective X chromosome. The actual ratios vary in different populations, and one book reported that color deficiency is more common in European stock, and much less common in Asian and Native American. (Perhaps northern dwellers during the ice ages did not need color vision as much and lost it during a mutation?)
Color deficiency can be a real problem.
It can be dangerous when driving, and is often first diagnosed when people apply for a driving exam. It can have great impact on some careers -- electronics and flying especially.
Color deficiency in school
With an average of one boy in every classroom having color problems, teachers need to be told, but in 29 years of teaching, I hardly ever had the the school tell me at the beginning of the year who might be color deficient. I think there should be mandatory testing. The 2nd most common form is total red-blindness, which means that such a person sees red correction marks as black!
There is a good story about a man who got good grades in a college of modern art, and didn't find out until after graduation that dogs weren't really pink!
Color vision is complex and difficult to test
It is useless to ask, "What color is that?" Most colorblind people are only partially colorblind, and learn to interpret subtle clues. They may see a yellow lemon as greenish-brown, but they have learned since a child that is what others call "yellow".
Designing Web Pages for color-deficient people
Since color-deficient is common, it is important to design web pages appropriate. The simple rule is to make backgrounds light and text dark If text is red, it may appear black, which is ok...unless the background is also black.
|Links about color and color deficiency
http://www.toledo-bend.com/colorblind/ -- lots of good material, and links
Firelily -- good analysis of web page design, in general and for color deficient people.
Visibone -- excellent source of color charts