Richard Ernst, age 9, of West Vancouver, B.C., Canada, for his question:
WHAT EXACTLY IS COLOR BLINDNESS?
Color comes in a lot of different shades and degrees of brightness. The National Bureau of Standards has determined that there are more than 250 different colors with about 7,500 common names to describe them. ''Hue'' is the basic name of a color while the word ''saturation'' refers to the amount of hue and "lightness" indicates how light or dark it is.
Scientists say that many animals, including cats, dogs and horses, probably do not see color as we see it. This doesn't mean that their eyes are defective since it is the normal condition for them.
Color blindness in humans is called daltonism. It means, simply, that some people are unable to tell all colors apart.
Most people who are color blind can only see two basic colors in a rainbow and they also tend to confuse other colors. If this is the person's problem he is said to have dichromatic vision. With dichromatic vision a person will see a wide range of yellows and blues but he will tend to confuse reds with greens, and some reds or greens 'with some colors.
Only a few people are truly blind to color. But it does happen with people who have achromatic vision. A person with this problem can only see shades of white, gray and black. Everything to him is like a black and white non color television set.
Men have more problems with color blindness than do women. Only one woman out of every 200 will have the problem, while about four men out of 100 are inflicted. Science has not been able to find any cure.
A lot of people with color blindness don't even know they have the defect. They have learned names for the colors they see and the fact that they have a problem doesn't hamper their daily activities.
Colored triangles, squares and other shapes are buried in a mass of dots on cards used in simple testing for color blindness. The Hardy Rand Rittler test, often called the H R R, and the Ishihara test are among the systems used to determine the type and degree of color blindness. The colored shapes vary in hue and intensity and an examiner can quickly determine a patient's ability to see various colors. A test called the Holmgren measures the patient's ability to match colors.
Color blindness is most likely inherited. A color blind man who marries a woman with normal vision will almost certainly have children with normal vision. But the defect will be hidden in the man's daughters and they will be able to pass it on to their children. If a color blind man marries a woman whose father is also color blind, probably half of his children will also be color blind.