Shades of gray: color blindness in men

by Jeff Siegel

A color television may not mean all that much to you. Red, white, and blue is an idea, and not necessarily something on the flag. You understand that green means go, but your realization probably doesn't extend much past that.

If you answered yes, it's because you probably have what is popularly called "color blindness" a genetically inherited defect that is as common as it is hard for people who see the full range of colors to imagine.

"There is a remarkable amount of misunderstanding about this most common and natural disorder," says Jay Neitz, PhD, who teaches at the Medical College of Wisconsin in Milwaukee. He and his wife, Maureen Neitz, PhD, are considered among the leading researchers in this field in the country. "The lack of understanding is not just among the general public, but also among teachers and other professionals, even though color is used ever increasingly as a tool in education."

Color blindness, in fact, is not blindness at all. Most people who are described as color blind can see colors. They just don't see the same colors the rest of us do.

"That's why, if I would call it anything, I would call it color deficiency," says Michael F. Marmor, MD, a professor of ophthalmology at the Stanford University School of Medicine in Palo Alto, California. "Color-blind people see differently, but they're not blind to colors."

In fact, there is a diversity to color blindness in the range of deficiency and the severity of the deficiency that still surprises researchers. People who can see all of the colors of the rainbow can distinguish between more than 100 hues (a hue being a technical term that means pastel green and plain green, although different colors, are the same hue).

Colorblind people, on the other hand, deal with an entirely different palette. Generally, there are two types of color blindness:

• Red-green
  • the most common.
• Blue-yellow
  • which affects only 1 out of 100 colorblind people.

These terms, incidentally, refer not to what can't be seen, but to the way the eye works in distinguishing color.

Someone with severe red-green color blindness, for example, can see only two colors. A so-called dichromat (which means "two colors") sees everything from red to green on the rainbow as yellow, and everything between blue and violet as blue. This means there are no intermediate hues—no aquas or turquoises. Instead, what isn't blue or yellow is part of a region devoid of color but not necessarily gray or white, since a dichromat may not have any idea what gray or white looks like.

If you are NOT color blind, try to imagine a pie chart in a textbook where each slice of pie is the same anonymous, indistinguishable color, a red stop light that looks exactly like an orange-sodium street light, or a mail order catalog where every pair of pants looks alike you'll begin to get the idea.

"One might think that one could learn about the perceptual world of color blindness by interviewing a colorblind person, but this often leads to more misunderstanding than enlightenment," says Dr. Neitz. "It is impossible for them to imagine what they have never seen so they can't relate their world to that of the person with normal color vision."

Dichromats are about one-quarter of the estimated nine million color-blind people in the U.S., almost all of whom are men. The rest are categorized as anomalous trichromats, whose color vision is somewhere between normal and dichromatic.

This wide range extends from anomalous trichromats whose color vision is nearly identical with that of someone who sees all 100 hues to the most deficient dichromat. An anomalous trichromat in the middle, however, can tell the difference between red and green, but gets stuck when asked to distinguish between olive green and brown.

Most colorblind people are men because the genetic deficiency is passed from mother to son in alternate generations. That means that if the mother's father was colorblind, there is a 50% chance her sons will also be colorblind The son's sons won't be colorblind, but if the son fathers a daughter, there's a 50% chance the son's grandson will acquire the deficiency.

Currently, there are no effective treatments or a single accurate test for color blindness, and there is an active debate in the scientific community about whether either is needed. Dr. Marmor, for one, almost never tests for color blindness, and the tone in his voice makes it clear what he thinks of treatments and cures. Things like pink-tinted contact lenses are "foolish and dangerous," he scoffs.

"It's just the way some people are," Dr. Marmor says. "I don't consider it a serious problem, and that's why I don't routinely test for it."

Dr. Neitz, on the other hand, points out that some sort of accurate measuring stick should be established, if only for those professions law enforcement, gemology, and people working with electricity, to name a few where distinguishing between hues is necessary.

"When color is used to teach second graders," he says, "the colorblind student will be overwhelmed. An enlightened teacher might recognize that the student is colorblind, but an unenlightened teacher might conclude that the child has a learning disability or an attention deficit disorder."

That's why the Dr. Neitzes are developing a two-fold test, featuring genetic screening (since the color genes of the colorblind are different) and a simple pencil-and-paper process.

If you would like to learn more about the genetic component of color blindness, or would like to try an informal color perception test, visit these Internet sites:

The Biology Project, University of Arizona:
Information about how color blindness is passed down from mother to son.