Power Point Tip: Effective Color Contrast

Designing for People with Partial Sight and Color Deficiencies

Partial sight, aging and congenital color deficits all produce changes in perception that reduce the visual effectiveness of certain color combinations. Two colors that contrast sharply to someone with normal vision may be far less distinguishable to someone with a visual disorder. It is important to appreciate that it is the contrast of colors one against another that makes them more or less discernible rather than the individual colors themselves.

Here are three simple rules for making effective color choices:

click on graphics to enlarge

1. Exaggerate lightness differences between foreground and background colors, and avoid using colors of similar lightness adjacent to one another, even if they differ in saturation or hue*. Don't assume that the lightness you perceive will be the same as the lightness perceived by people with color deficits. You can generally assume that they will see less contrast between colors than you will.

2. Choose dark colors with hues from the bottom half of the hue circle against light colors from the top half of the circle. Avoid contrasting light colors from the bottom half against dark colors from the top half. For most people with partial sight and/or congenital color deficiencies, the lightness values of colors in the bottom half of the hue circle tend to be reduced.

	3. Avoid contrasting hues from adjacent parts of the hue circle, especially if the colors do not contrast sharply in lightness. Color deficiencies associated with partial sight and congenital deficiencies make it difficult to discriminate between colors of similar hue.

*Hue, Saturation, Brightness. A method of describing color. Hue is the color itself; saturation is how pure the color is; and brightness is how light or dark the hue is.

Source: Lighthouse International. See http://www.lighthouse.org/text_only/t_color_contrast.htm for more information.

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