Imagine your life experience if you saw the world in limited color ranges. Imagine sitting in front of your computer surfing the Web. Most of the pages you visit are illegible because the information is presented for normal eyes only. You can’t see some of the links, can’t read a great deal of the text, and the graphics-there are graphics?! Welcome to the world of the color-blind; it’s not just about driving anymore! Chuck Newman addresses Web usability for the color-blind in “Considering the Color-Blind,” Web Techniques, August 2000.
Some form of color blindness affects 8% of men and .5% of women. Being color-blind is not like seeing black-and-white TV. Cones in the eye sense a range of wavelengths in red, green, and blue. In the color-blind, cones are genetically “wired” abnormally and react to a different range of light than they should. Other causes of color-perception problems include tumors, aneurysms, and glaucoma.
There are two types of color sensing deficiency: dichromacy and anomalous trichromacy. A dichromatic person has weakness or severe shifting of the wavelengths sensed by the cones. An anomalously trichromatic person perceives red shifted into green or green shifted into red. Ninety-nine percent of people with either type of color blindness have trouble with red and green. For example, when a dichromatic person sees a green object or text, the green and red-shifted-to-green cones make the object or text appear to be yellow. If the green object or text on a Web site is on a yellow background, the object or text disappears!
Newman suggests two methods of becoming temporarily color-blind yourself. To see what your images look like to a color-blind person, try uploading your images to Vischeck <vischeck.com>. Vischeck uses formulas to adjust the colors. The formulas come from “Digital Colourmaps for Checking the Legibility of Displays by Dichromats,” by Françoise Viénot, Hans Brettel, and John D. Mollon in Color Research and Application, August 1999.
Another slightly less accurate method of seeing how your images would look to the color-blind uses Paint Shop Pro 4 or 5.
1 Open your image in Paint Shop Pro.
2 From the Colors menu, choose Channel Splitting and Split to RGB. Three grayscale images are created.
3 From the Colors menu, choose Channel Combining, and Combine from RGB.
4 In the Channel Combining box, remove the check for “Sync blue and green to red.”
5 Choose blue in blue, green in green, and red in green. Now you can see how your images would appear to a color-blind person.
In a survey, Newman asked a color-blind population to evaluate some popular Web sites. Respondents stated that too many Web sites are hard for them to read. For more information, his survey and color-blind questionnaire page is located at <www.newmanservices.com/colorblind>. Newman has the following advice for designing Web pages using colors that can be seen and understood by all:
Black and white work best.
Initially design your page with black and white, using image, shape, positioning, and text for emphasis.
Use links with an underline or other graphic such as an arrow; links that consist of only a different colored word within a string of text and no underline are not perceived as links at all. (A visual cue, please!)
Links as a menu on one side of the page are helpful.
If you currently accommodate visitors with older 256 color or 640 x 480 pixel screens even though they make up fewer than 5% of current Web surfers, you should also consider accommodating the 8.5% of the population having some form of color blindness.