HTML and CSS Reference
In-Depth Information
Figure B-4
Types of color blindness
Color combinations that are easily readable for most people may be totally unread-
able for users with certain types of color blindness. Figure B-5 demonstrates the acces-
sibility problems that can occur with a graphical logo that contains green text on a red
background. For people who have deuteranopia, protanopia, or achromatopsia, the logo
is much more diffi cult to read.
Figure B-5
The effect of color blindness on graphical content
To make your page more accessible to people with color blindness, you can do the
following:
• Provide noncolor clues to access your page's content. For example, some Web forms
indicate required entry fi elds by displaying the fi eld names in a red font. You can
supplement this for color blind users by marking required fi elds with a red font
and
with an asterisk or other special symbol.
• Avoid explicit references to color. Don't instruct your users to click a red button in a
Web form when some users are unable to distinguish red from other colors.
• Avoid known areas of color diffi culty. Since most color blindness involves red-green
color blindness, you should avoid red and green text combinations.
