Tip #9

Color blindness

Color blindness is the inability to perceive colors in a normal fashion. It is an inherited condition that is sex linked recessive. As a result, very few women are color blind but approximately 1 in 10 men has some degree of color blindness. The most common form of color blindness is red-green (inability to distinguish red and green). There is a wide range of variability within this group from very mild to extreme. The second most common form is blue-yellow, and a red-green deficit is almost always associated with this form. The most severe form of color blindness is achromatopsia, the inability to see any color, and is often associated with other problems such as amblyopia (lazy eye), nystagmus, photosensitivity, and extremely poor vision. (Source: The Excite Health website).

To see an example of a test for color blindness, go to
www.toledo-bend.com/colorblind/Ishihara.html.

Because the manifestations of color blindness are so varied, it is difficult to prevent using colors that some of the audience cannot see. In general it is how these colors are used, particularly if they are used against each other, that results in problems.

Do not use red/green/brown/grey/purple next to, on top of, changing to red/green/brown/grey/purple. Furthermore, use contrast between colors.

Try viewing your page with a monochrome monitor setting. If the elements of the page are clear there, a color blind person will probably be able to work with your site.

Another point of advice is to NOT use colors by themselves to convey meaning or give directions to users. For example, you would not want to have a site with plain red buttons to imply stopping or green buttons to imply continuing. Nor would you use something like "These are our publications - those with a red bullet have been published in the last 6 months".

As I have mentioned, there are many types of color blindness, but the most common is red-green. Vischeck located at www.vischeck.com allows you to enter a URL and it produces a copy of the page as it would appear to someone with red-green color blindness. I encourage you to go to this site and enter a URL for a site that has red or green on it, such as http://cals.arizona.edu/pls/ or http://arizonaathletics.com/ and see how this page displays to someone with red-green colorblindness.