This section is from the "The New Student's Reference Work Volume 5: How And Why Stories" by Elinor Atkinson.
There are a certain number of people in every hundred whose eyes seem to be perfect except in color seeing. One doctor has discovered that one person out of every fifty-five cannot tell red.from green. One in sixty confuses brown and green. Pink and yellow look alike to some people, and blue and green to others. To a very few people everything looks to be black and white. The cause of color blindness is thought to lie in the nerve fibres in the retina, or screen at the back of the eye, on which pictures are thrown. Three nerve fibres are supposed to give sensations of red, green and violet Orange, yellow and blue are seen by combinations of sensations. Now one of these fibres, most often the red, may be non-sensitive. That person will not see red at all. White to him appears bluish-green, with the red rays in the white absent. Violet looks blue, orange yellow.
In some cases there may be a total absence or paralysis of a nerve fibre sensitive to a certain color. But in a great many cases, it now appears that a defective color sense can be developed by proper education, just as the sense of form, size and distance can be educated. Perhaps you have wondered why brightly colored cards, pegs, wools, crayons and paper weaving-mats are used by the children in kindergartens, and in the baby grade in school. Teachers find little children as clumsy with their eyes as with their fingers. Many little children appear to be tone deaf, also, although hearing perfectly otherwise. It was a wonderful discovery in education that our five senses can be developed and trained. Thoughtful people noticed that women see colors better than men, as a rule. Girls have no better eyes than boys, but their interest in dress, house furnishings and flowers, brings colors into their daily lives. In France there are men silk dyers in factories whose color sense is so developed by use that they can grade sixty shades of gray.
Perhaps some boys who read this may think color of little importance in business, except to artists, decorators and dyers. Well, a farmer who could not see red would not be a good man to pick cherries. And how about signal lights on railway lines, lighthouses, bridges and in mines? Some wrecks are thought to be due to the inability of the engineer or pilot to tell red from green. Many railroads now examine the eyes of train men to detect color blindness. Since experiments show that the sense of red is most apt to be absent, it would seem that red signal lights should not be used at all. Green and violet are said to be least often confused. To the man blind to red rays, violet appears to be blue. It would be an interesting game for you to test the color-seeing powers of yourself and of your family and schoolmates. It could be done by cutting up a set of kindergarten weaving mat papers and pasting the strips on sheets of white paper. Each person should have a sheet and be required to label the colored strips in writing.