What is color blindness?

The other day I was at a party, making friendly but uninspired small talk with the host’s son. Most attendees, including the two of us, had been struggling to start interesting conversations, as we all didn’t know each other very well. At one point, the color of something or other came up. I mentioned that I’m not good with colors, because I’m color blind, and our conversation livened up. The host’s son knew a thing or two about color blindness, because his dad is color blind too, and he wanted to know how my vision compared to his dad’s.

This instance reminds me of a former coworker who is deaf in one ear. When she mentioned this to people, she would get much the same reaction. People ask what it is like and what problems it poses in daily life. I don’t know about being deaf in one ear—I think it takes more effort to deal with than color blindness—but I know what it’s like to be color blind.

What it is like to color blind

As you might expect, color blind people tend to figure out at a young age that they are color blind. Or maybe someone figures it out for them, such as their primary school teacher, who realizes that Little Peter often grabs the pink pencil when he’s supposed to be coloring in blue.

Sadly, I don’t remember when I found out that I have color blindness. It may very well have been when I was a poorly coloring toddler. But I do remember that one day in primary school I did an Ishihara test. You may have seen it before: it’s the test where someone asks you to look at a circle consisting of many smaller, colored circles and to tell them what number you see in the big circle. For instance, some of the smaller circles may be blue, and others—in the form of the numeral six, say—may be purple. People with normal color vision would see the number six, while a color blind person who cannot see red would see zip. If I didn’t know I was color blind before that day, I knew then.

An Ishihara plate

An Ishihara plate. I don’t see any numbers. What do you see?

Color blind people experience a variety of problems, but fortunately they tend to be relatively mild. Perhaps the most serious effect is that color blind people can’t hold certain jobs. For instance, in many countries, a color blind person cannot become a commercial pilot, because there are important red/green signals in aviation and many color blind people cannot distinguish between them. You don’t want your pilot thinking it’s safe to land when an indicator light tries to tell him that the landing gear is stuck.

Color blind people also generally do not make good electricians, because electrical wiring is often color-coded. In fact, many things in life are color-coded. If you pay attention to color coding for a day, you might be surprised how much humans rely on color.

Then there are the effects on daily life that I would describe as mildly annoying. For example, it can be difficult to buy clothing whose colors “match” according to people with normal color vision. And on a basic level, color blind people simply cannot enjoy color as much. Are we in the season of Indian Summer? All the leaves still look green/brown to me, as they always do. Thankfully, this particular problem may be solved in my lifetime—more on that later.

Left: an Indian Summer scene. Right: a simulation of the way a person with protanomaly would see the scene, by the Coblis color blindness simulator.

Other examples of the effects of color blindness in daily life include:

  • When I charge my e-reader, a charging light comes on. Supposedly the light changes color when the device finishes charging, but I can’t tell. I simply let the device charge for a few hours and assume that will be enough.
  • Some public toilets indicate whether they are occupied or available only with a circle that is red or green, and I often can’t distinguish between the two. Toilets in airplanes are the worst offenders.
  • When I’m in the grocery store buying bananas, I have no idea what I’m doing. My significant other claims I always buy the green ones, which in a way is impressive, because I can’t tell green bananas from yellow ones.

How color blindness works

People often ask me, “If you’re color blind, which colors don’t you see?” The answer is a little more complicated. Our eyes include receptors, the so-called cones, that can perceive light with wavelengths in a certain range. There are three types of cones, called the short (S), medium (M), and long (L) cones, named for the range of wavelengths of light they are sensitive to. For instance, short cones are (mostly) sensitive to light with a short wavelength. The wavelength of light determines what color we judge the light to be, so each type of cone can “see” a certain range of colors.

And there are many forms of color blindness. In the most common forms, one of the three types of cones is absent, producing dichromacy, or functions poorly, causing anomalous trichromacy. I have protanomaly, which is a form of anomalous trichromacy. It affects roughly one percent of men and it is not the most common form of color blindness, but it also isn’t rare. Fortunately for me, protanomaly is a relatively mild form of color blindness.

In the eyes of people with protanomaly, the L cones, which are supposed to be the best at perceiving red light, don’t function well. So you can think of it as me having a hard time seeing the red component of colors. For instance, if you show me a blue shirt and a purple shirt, I might not be able to distinguish between the two, because purple consists of a mix of blue and red. Or I might be able to distinguish between them only based on the shirts’ brightness, but not based on their hue. It depends on the exact colors. Dichromats, whose red receptors are absent entirely, have the same problem, but worse.

Another popular question is whether I, or other color blind people, can see any color at all. I can, and so can most color blind people, but there is a small minority of monochromates, who see only 50 shades of grey. I kid, I kid. They see infinite shades of grey. But they don’t see any color, so to them life appears as a picture on a black-and-white television. This type of color blindness is very rare and makes life difficult.

The incidence rate of color blindness

Color blindness is less common than other vision problems, such as nearsightedness. But around eight percent of Northern European men carry some form of color blindness, so you will likely know some color blind people. The rate among women is lower: on the order of one percent. So in total, color blind people account for four to five percent of the population.

Color blindness is more common among men than among women because most forms of color blindness are hereditary in such a way that men are more likely to receive color blindness genes. In particular, the genes that cause the most common types of color blindness are passed on through X-linked recessive inheritance. That means color blindness genes reside on the X chromosome, of which men have one and women have two. When a man receives an X chromosome with a color blindness gene from his parents, he will be color blind.

But when a woman receives one X chromosome with a color blindness gene (or “defect”) from her parents, she will not automatically be color blind. She will only be color blind if her other X chromosome also has that defect. The odds of both X chromosomes having the same color blindness defect are smaller than the odds of only one X chromosome having such a defect, so women are less likely to be color blind.

Graphic demonstrating X-linked recessive inheritance

An illustration of X-linked recessive inheritance. Modified version of a graphic by the National Institutes of Health.

Mitigating color blindness

What can we do to mitigate the effects of color blindness? When one in 25 people can’t see whether a toilet is occupied or available, that’s a design failure. Yet this type of red/green signal is everywhere. To help color blind people, you can and you should avoid using “green means good, red means bad” indicators. Instead, use a combination of blue and red, or blue and yellow. The vast majority of color blind people can see blue well and will be able to distinguish between these pairs of colors. Of course, not relying on colors at all is an even better design choice.

People who are color blind routinely remedy these minor inconveniences. For instance, I ask my significant other whether this or that shirt goes with such and such pants. I know the red traffic light is the one at the top, and when I play board games with friends, we try to pick pieces with colors that I can easily distinguish. But we color blind people would appreciate if designers helped us out.

What about the underlying issue? Can we improve color blind people’s ability to see color in the first place? A few years ago, a California company called EnChroma made progress on this front. The company developed glasses that partially correct color blindness for people who have trouble seeing reds and greens. Their glasses cut out some wavelengths of incoming light in such a way that after the color blind person’s eyes process the light, the color is closer to what a person with normal color vision would see. This idea isn’t new—a friend of mine thought this up years ago, and I’m sure others have too. But EnChroma made it work.

How well did they make it work? You can find videos of people putting on a pair of EnChroma glasses for the first time and bursting out into tears, claiming they can see colors they have never seen before. Those videos are great marketing, but do they accurately reflect what the glasses would do for most color blind people? It’s unclear.

EnChroma’s technology is new and not nearly as effective as the lens technology that helps your grandpa read the newspaper. For instance, EnChroma estimates that there is a 75 percent chance that their glasses will noticeably improve color vision for people with protanomaly, such as me.

The company’s glasses are much more effective in broad daylight than indoors. They work well when you’re walking through the forest in Indian Summer. That’s because EnChroma’s technology cuts out some light, so it helps for the incoming light to be bright—there needs to be light left for you to see. Sadly, for the same reason, everybody’s color vision, including that of color blind people, is better outdoors and worse indoors. So the glasses help least when we need the most help.

Still, EnChroma’s efforts are a good start and I am grateful that the company is developing glasses for color blind people. I am inclined to wait for their technology to improve before I give it a shot; I want EnChroma glasses version 2.0, so to speak. But I hope they come soon.

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Posted by Peter

Here, Peter writes about whatever has caught his interest recently. Maybe he'll narrow down this blog's scope someday.

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