CS 552 - Color Coding Guidelines

CS 552, Spring 1998

Color Coding Guidelines

Derived from Richard E. Christ, 1975, "Review and Analysis of Color Coding Research for Visual Displays," Human Factors, Vol. 17, No., 6, pp. 542-570.

(1) Avoid "false coding," where the association of particular colors implies relationships that do not actually exist.

Explanation: Some colors have emotional associations that should not have to be un-learned. Avoid their use in arbitrary contexts, so as not to confuse and frustrate users.
Example: Red/yellow/green should not be used to identify qualitative groups (e.g, democrats vs. republicans vs. independents).
Exception: "False code" colors can be included as part of a broader spectrum of colors, since the association will be diluted.

(2) Use the four "focal colors" to encode information that needs to be remembered.

Explanation: The focal colors (red/blue/yellow/green) are easily discriminated, and unlikely to be confused with one another. They are also easily remembered and recognized by individuals from most cultures.
Example: For a series of related graphs or other images than encode information (e.g., maps showing different densities, bar charts comparing values from different subsets of a population) use these colors so that the user can quickly distinguish the values for each subset.
Exception: Be careful not to imply a false relationship among red/yellow/green. If there are three values to be coded, deliberately choose blue as one of them to break the cultural associations with red/yellow/green.

(3) Avoid subtle distinctions in color codes.

Explanation: The difference between to similar colors may be discriminable when the colors are adjacent, but will easily be lost when colors are intermittent in a display. The difference between perception and reality means that a users may not see the color correctly, or may "see" a color that isn't really there.
Example: Colors that are close to each other (e.g., red and orange of a similar brightness and intensity) are easy to confuse when they are not adjacent to one another. If they must be used, vary the colors along multiple dimensions, changing the brightness and intensity as well as hue (e.g., bright red but pale orange).
Exception: A closely related spectrum may be desirable to indicate subtle variations in values, such as a map showing temperature gradations. Beware that users may misinterpret particular values, however.

Prepared by C. Pancake, March 31, 1998