John Dalton was a famous chemist in the 18th Century. Yet, he was a man who described blood as æbottle greenÆ, and considered a laurel leaf as a good match for red sealing wax. Fortunately, others in his field recognized that Dalton was suffering from color blindness, or, more correctly, defective color vision. Dalton became so well known with his faulty applications of color in his work that in some parts of the world color blindness is referred to as Daltonism.
 
All the colors can be made by mixing three primary colors: red, green, violet, or yellow or blue. For instance, colors of flowers are created by combination of granules of pigments having the three primary colors of red, blue and yellow. Because of the cone cells in the retina of the eye, which are sensitive to red, green and violet, our eyes are able to reproduce all the colors in nature for us.
What happens when a person is color-blind?

Certain colors strike the eye and fail to create the sensations which they reproduce in normal eyes. For example, rays of red light strike the eyes and not only stimulate the parts of the retina that are sensitive to red, but also stimulate those parts that are sensitive to green.
 About 1 in 20 people are affected by color blindness. So, why do they see color differently than others? Well, a person sees normal colors if three beams of light û red, green and blue û are combined in equal proportion to produce white light. When those three beams of light are combined in unequal proportions other hues of color are produced. Yet, a color blind person is only able to. Mix two of the primary colors. Such a person is known as a dichromat, being defective in one of the primary colors. For example, a person may be a green blind dichromat. A more serious condition is that affecting monochromats. These people have no color discrimination at all. For them, life is seen in black and white. The majority of those affected by color blindness, however, are what are known as anomalous trichromats. These people are still able to see hues produced from the three primary colors, but the proportions that they see are distorted.
Why do these people see things differently? It comes down to light receptors, or cones, of which there are about 130 million. About 7 million of these are applied to our color vision. There are three types of cones that operate in people with normal color vision û those that respond best to long wavelengths of light (blue), those that respond to middle wavelengths (green) and those that respond to short wavelengths (yellow). Damage to the optic nerve that affects the conesÆ message to the brain can cause color blindness. It has been shown that certain chemicals and stimulants, such as alcohol, tobacco and oral contraceptives can also affect color vision. The aging process can also affect color perception, especially with regard to blue light. Most colorblind people however, are born with the defect.
 Color blindness is a sex linked genetic disorder, transmitted by females but usually appearing in alternate generations of males. If you are born color-blind, then, it is likely that your grandfather had the same condition.
A person may be slightly color-blind, and this can be unknown to anyone, including himself. A person who is red-green color-blind can learn at an early age to tell the two colors apart, even though he sees both colors a grayish-yellow. He doesn’t do it by color, as people with normal vision do, but by judging the tone and luminosity of what he sees. Red and green have quite different luminosity. Avoid excessive use of alcohol or tobacco, as this will further deteriorate your already faulty vision.