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On This Page:  • Six Discrimination and Identification Color Guidelines

Discrimination and identification difficulties can arise when colors are used for grouping and labeling. The colors of two patches are discriminable if the user can tell that they are two distinct colors. A color is identifiable if the user can tell which of the coding colors it is. In some applications a legend is provided to aid identification, in others not.

Use no more than six colors to label graphic elements. How many can be reliably identified depends on several characteristics of the application. In cockpit and automotive applications the user can afford only a glance at the display as part of a rotation among items that must be monitored, and errors can have severe consequences. Fewer and highly distinct colors must be used in this type of application. On planning displays (e.g., maps, scientific visualizations) the user typically has time to more carefully scrutinize elements and refer to a legend. The consequences of errors are less immediate and more likely to be noticed before there are problems. Often more colors can be used in these cases.

Visual and cognitive aspects of the display itself also influence discrimination and identification of colors. These include such factors as size of symbols and opportunities for visual comparison with legends and among symbols.
More about discrimination and identification of colors.

red green-blue
red-orange cyan
orange blue
yellow-orange purple
yellow blue-magenta
yellow-green magenta
green red-magenta
  Look over these colors and their names to the left. Now click here to test your ability to identify some of the colors on the left.

The test is made difficult by such factors as the fairly narrow stroke width, the spatial separation of the colors and the absence of a legend showing all the colors and their identities.
In this context 20 colors are usable: A map of the United States utilizing a variety of colored areas and lines to indicate weather patterns. Different luminances of a hue are used to indicate different levels of weather conditions. The reulst is an appropopriate use of 20 different colors.
Larger Image New Window.
A colored map using a continuous range of colors to indicate terrain type.
Larger Image New Window.
Continuous-tone color codings (e.g., terrain elevation in this chart) aren't addressed at all by the usual guidelines. While a color legend is included, detailed information about terrain elevation is given by the redundant contour lines with their numerical labels.

Use colors in conformity with cultural conventions. Some hues have become associated with particular meanings through widespread use or tradition. Red, yellow, and green are associated with safety status. Other uses of these colors can lead to unintended interpretations.

In applications where only six-to-eight colors are identifiable this severely restricts the options for color coding of non-safety variables.

Conformance with safety coding conventions can be a challenge when multiple hazards have to be displayed simultaneously. Consistency of usage, coding conventions, and luminance contrast requirements can be in conflict. For an example of such a conflict and one proposed solution, look at our Design of Cockpit Graphics Example.

Use color coding consistently across displays and pages. Users should not be required to associate different meanings with the same hue in various parts of their work environment. Remembering different interpretations in different contexts increases cognitive effort and opens opportunities for error.

Use color coding redundantly with other graphic dimensions. When user populations may include users with anomalous color vision (8-10% of the population), important information must be identifiable on some basis other than color discrimination. Even for color normals this can be a valuable design goal.
More about individual differences in color vision.

The elements within these sets look identical to deuteranopes, the most common kind of dichromat: 2 sets of 3 colored squares on a black background. Both sets look identical to deuteranopes. These can be discriminated on the basis of non-color differences: 2 sets of 3 colored shapes on a black background. The shapes include a triangle, square and circle, allowing deuteranopes to distinguish the symbols.
Don't use color coding on small graphic elements. Color discrimination is better for large areas than for small (e.g., small fonts and symbols). This is more of a concern for "at-a-glance" applications than for those where careful examination is possible. Even in the latter it can slow the user down.
More about discrimination and identification of colors.
Series of dots from large to very small. The color of the smallest dots is hard to distinguish.

Use neutral gray surrounds where color judgments are critical. Simultaneous and successive color contrast can interfere with accurate color identification.

2 identical magenta squares on a white background. The 2 squares appear the same color. 2 magenta squares on 2 different color saturated backgrounds. The magenta sqaure on a pink background appears more blue than the magenta square on the green background.

In the figure on the left the physically-identical blue squares appear the same. In the figure on the right the appearances of the physically identical squares are different due to visual interactions between the squares and their differently colored backgrounds.
More about simultaneous and successive contrast of colors.


Which color is this?
Which color is this?
Which color is this?

Back to the color names Back to the top of the page.

Related Topics:
go to this page Color Discrimination and Identification
go to this page Grouping with Color
go to this page Labeling with Color

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