Websites for the Colorblind
Does your website care about 15% of its visitors?
With up to 15% of the population being affected by one form or another of colorblindness, everyone who does a website should be asking the question: Is it worthwhile to make sure my site is workable for these people? While I can't imagine an answer other than "YES!", even if your answer is "no", you should consider these guidelines because they also make a visit to your website better for people with normal color vision.
A Note on Handicapped Accessibility
More and more websites are working to be accessible to the vision impaired - as opposed to those who have a color vision deficiency, but otherwise have normal eyesight. While this website supports that goal, there are already organizations working for that and it also involves a great deal more complexity. This site is concerned strictly with color vision deficiency.
Speaking For The Colorblind Of The World
OK, I wasn't elected... but since I have a forum, I will present some ideas at least on behalf of the colorblind. The things that make it easy on people who are colorblind are also very good for those who are not colorblind. The only drawback is for those who want to use "unconventional" color schemes and, in a few cases, conventional colors that aren't implemented well. Following are some examples of practices to avoid if you want your website to be friendly to all of your visitors.
Very Common and a REAL PAIN!! ERRORS MARKED IN RED
When filling out a form on a website, it is often easy to make a mistake. Typically, the form is checked when you submit it to see if all of the information appears to be valid. If you make a mistake, the form comes back with wording to the effect of: "Please fix your entries in the fields marked in red" Just one problem... You've got me seeing red because I CAN'T SEE THE RED!
Black & White text provides good contrast and is easy for everyone to read. It is also typically pretty fine and frequently small, as well. So, colorblind people can see the text well enough - light & dark / contrast. But, there isn't enough red to see the red - it is dark just like the black. If it were blue, we'd see it right away. But, red is the standardized color for errors. If the red text is made BOLD it becomes easier for anyone to pick up on and possible for colorblind people to see because now there is enough red present to pick it up.
Low Contrast Content
Good web design practice, in general, demands a reasonable amount of contrast between foreground and background. When you have a colorblind visitor, this becomes critical. I have seen pages that I thought would never load... or were just blank. At the same time, expecting there would be content and noting that the background was red or black, a close examination revealed there was, indeed, something there... it was just set up in colors that made it nearly impossible to find. In the best case, low contrast is difficult to read; in the worst case, it can't be read.
Displaying content with gradated colors, as is often done for graphs and some charts, is another case of the same thing. Unless each color that signifies something is substantially different than the next, they will pretty well blend in for someone with color deficient vision. Why? After all, they are different colors! Well, gradated colors are going to contain elements of red and green. If someone is red/green colorblind, these elements will not be visible and everything looks like it is the slightest shade lighter or darker than the next item. Even then, a differentiation can be made - but only if the two are next to one another. Separate them and the difference is lost.
Certainly, these are not the only problems people with color deficiency experience with websites. But, these are the most common.