How Do Color Blind People Perceive Color?

When we talk about building accessible web applications, we don’t imply that everything should be converted to text-only pages. Color and imagery are necessary and fine as long as we understand how color blind people—who constitute a wide audience on the web—perceive color.

There exists a misconception that color blind people see no colors at all. These people, called achromats, are an extremely small group. A much bigger number of color blind people (1 in 12 men, and 1 in 250 women) have red-green deficiency, and do see color except certain color combinations may appear confusing to them. For example, both red and green appear as dark brown to black and therefore should be used with caution, while orange and blue actually look as orange and blue to them, and therefore are safer.

While researching the subject of how exactly color blind people see color, I came across a very interesting paper by two Japanese researchers, entitled How to make figures and presentations that are friendly to color blind people. I was fascinated by the depth of their research, and recommend you read it very carefully. No vicious pun intended, but it was a true eye opener.

The researchers explain which color combinations are confusing to color blind people, and which are safe. For example, instead of using traditional dark red (#f00) they suggest vermillion (#f15a22). Or if you have to use green and red, make sure they contrast enough with other colors, which is also explained in the paper.

On a related note, there’s another interesting whitepaper at the University of Maryland web site, Color Vision Confusion, with a great many links for further reading.

To see how your web site appears to people with red-green deficiencies, head to an online service called VisCheck.

I’ve found so many outstanding articles, online services and downloadable tools, that I could sit here and list them all night. What are your favorites?