For people who lack certain perceptual sensitivity (incorrectly called color
blindness), you can work at testing the colors you are choosing to make certain
that they can be easily distinguished from each other. Particular problems occur
telling the difference between red and green for instance. Always design the screen
or form with alternative cues, such as icons, written text, or audio cues that reinforce
the content. For instance if a hyperlink that has been clicked on turns blue to
show it has been followed, you can also add another icon to the display to indicate
that it has been followed or create a separate sidebar list that shows which Web
sites have been visited. These are better alternatives than relying solely on color to
convey your message.