Around the same time your baby is consciously reaching and grasping, he undergoes a gradual transformation that is as remarkable as the scene in The Wizard of Oz when Dorothy leaves the black-and-white world of Kansas for the brilliant colors of Oz. The red, blue, and green cones in his retina come online. All the rainbow of colors we see is a combination of these three primary colors of light.
There is nothing inherent about the primary colors that makes them primary – it is only that we have these three types of cones, and that the entire rainbow spectrum of visible light can be coded for by using only these three reference points. Another species could use a different number or group of colors as primaries.
More than five million cones line the postage stamp of tissue at the back of the eye we call the retina. More than five megapixels. The result is that the eye is able to pick out a pinpoint of color. As quick as a glance, the patterns change, and the eye is able to seamlessly generate another precision picture of the world around us.
As the world of color emerges, this palette will color your baby’s choices of where to gaze, what to reach for, and what to play with. For about 1 in 25 people (including one of my children), some or all of the cones do not come in, resulting in some degree of color blindness. By far the most common type is red-green color blindness. Color blindness is usually tested for at children’s four-year-physicals, but it may be suspected earlier since color blindness is almost always a hereditary condition.
Red-green color blindness is a recessive condition passed on the X chromosome. Only one healthy color vision gene is necessary to provide color vision. Since boys have only one X chromosome, it is much easier for them to be color-blind. If their mothers are carriers (having one normal X chromosome and one color-blind X chromosome), the sons have a 50 percent chance of having the condition. Red-green color blindness occurs in about 8 percent of American males. These men cannot pass the condition on to their sons (since they give their sons a Y, not an X, chromosome), but they will pass the gene to their daughters.
All girls whose fathers are color-blind will at least carry the gene for color blindness. In order for a girl to actually be red-green color-blind, she must have a mother who is a carrier AND a father who is color-blind. This happens in only about .64 percent of American girls (although these numbers vary considerably in other populations groups).
By being aware of their condition, we can help our children learn other ways to distinguish between red and green – the position of traffic lights, for instance. And we can decorate their worlds and wrap their presents in the millions of nuances of color that are still available to them.
This is an excerpt from: From First Kicks to First Steps: Nurturing Your Babys Development from Pregnancy Through the First Year of Life, McGraw-Hill, 2004, P 245