I’ve always believed that web site accessibility depends on an understanding of accessibility issues — not on technical issues. Obviously, knowing the technical side of web site construction and how it impacts accessibility is very important. Some decisions are fundamentally technical, but a huge part of web site accessibility is purely visible — and just understanding accessibility issues will make a huge difference.

To that end, here are a few quick comments about color blindness. Color blindness (or color perception deficiency) is an issue for approximately 1 in 12 people, mostly men. However, color perception problems are not always very effectively diagnosed, so these numbers could be low.

Color blindness is an inability to see certain colors.

Color blindness is really a misnomer. People with various types of color blindness are better described as being color vision deficient: it’s an inability to distinguish colors, not an inability to see color. People at the furthest limits of color deficiency, however, may have such an extreme inability to discern colors that this can be a fairly accurate description.

Individuals with color vision deficiencies can’t see red.

Well, no. Assuming we’re discussing Protanopic or Deuteranopic color blindness, in which the individual is missing either the red or green sensitive cones, the actual problem is that they may not be able to distinguish the color red. The color isn’t readily differentiated from other hues of the same shade or tint. Red perception deficiency is certainly the most common type of color vision deficiency, but it’s certainly not true of all individuals with poor color vision.

You have normal color vision

Not really. In fact, color perception is a spectrum for all of us. What’s commonly referred to as color blindness is actually only the portion of that spectrum which is considered anomalous — where the ability to perceive color begins to impinge on normal interactions with the world. Having “normal” color vision simply means that you don’t generally experience problems because of your color vision. You may well still fail an Ishihara test.

Color perception deficiencies are inconvenient, but don’t pose any serious problems

Particularly in our modern, technological society, color perception is a critical part of comprehending the world around you. From LED indicators which blink red, green, or yellow; to weather maps which a spectrum from red to green indicating storm severity; to knowing what color a traffic signal is showing if you’re in a location with a different signal orientation than what you’re familiar with. Outside of technology, color deficiencies can impact recognizing that you’re developing a severe sunburn or knowing whether you’ve actually cooked that hamburger enough to be safe.

People with Color Perception Deficiency have better Night Vision

Actually, I couldn’t definitely verify this one way or the other. There are a number of claims that this is true, but the reasoning is highly variable and not particularly evidence-based. It’s possible that certain types of color perception deficiency may give people better night vision, but it’s also possible that since some types of color perception deficiencies cause people to be photosensitive, those people may feel like their night vision is better, simply because it’s much better than what they’re accustomed to. Regardless, any evidence which is reasonably definitive would be appreciated.

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