Accessible use of color in figures

Color can serve both communicative and decorative uses in figures.

Students preparing a figure for a course assignment may use color provided that the assignment will be delivered in a format that supports it.

Authors seeking publication should avoid the use of color except when it is necessary for understanding the material because of the relatively high cost of color reproduction for printed materials. If color representation is not crucial for understanding and the article is to be published both in print and online, convert the figure to grayscale or consider placing the figure online as supplemental material. Some journals offer the option to publish a figure in color online and in grayscale in print at no cost; when using this option, ensure that the figure can still be understood even when it is printed in grayscale. Authors submitting a manuscript to an online-only journal may use color more liberally (e.g., colored bars rather than gray and white bars in a bar graph).

When selecting colors for a figure, ensure that there is plenty of contrast so that people living with a color-vision deficiency (often referred to as “color blindness”) or people who do not see color in a typical way can understand the information and tell the colors apart.

Best practice is to use a contrast checker such as the free Colour Contrast Analyser to evaluate the contrast ratio and confirm that your content passes the standards for WCAG 2.0 Level AA or later. Adequate contrast ratios ensure that the figure is not only accessible to readers with color-deficient vision but also understandable by all readers if the figure is printed or photocopied in grayscale.

Another strategy to achieve adequate contrast is to use a pattern in combination with color so that the differentiation of elements does not rely on color alone (e.g., in a line graph, different lines may be in different colors and also of different styles, such as solid, dashed, and dotted).

When many colors must be used and it is not possible to achieve high contrast among all of them, label colored areas directly in the image or use lines to connect the object to its label rather than placing the label in a legend, if possible. When you use this strategy, readers do not have to match colors in the figure to colors in the legend and the figure can be made more accessible.

The following figures show examples of how people with a certain color-vision deficiency see color and how the colors used in figures can be adjusted to accommodate them to make the figures accessible. The type of color-vision deficiency demonstrated here is called deuteranomaly, which is a reduction in sensitivity to the green area of the spectrum. It is the most common kind of color-vision deficiency. Note that the data in the graphs are for illustrative purposes only; they do not reflect real participant information.

This material on color contrast was prepared with the assistance of accessibility experts at David Berman Communications.

1. Figure Without Adequate Contrast

The following figure does not have adequate color contrast. Panel A may look acceptable to someone with normal color vision but cannot be easily read by someone living with color-deficient vision. Panel B shows what Panel A would look like to a person with color-deficient vision. Someone living with color-deficient vision would find it difficult to tell from the legend which line represents the United States and which line represents Germany when looking at Panel A.

Figure 1

Student Happiness Ratings as a Function of Year and Country of Origin

2. Figure With Adequate Contrast

The colors in the original figure have been adjusted to provide adequate contrast. Panel C shows how the figure would look to someone with normal color vision. Panel D shows what Panel C would look like to a person with color-deficient vision. This figure has used color accessibly because it has adequate contrast. There are now distinct light, medium, and dark colors. 

Figure 2

Student Happiness Ratings as a Function of Year and Country of Origin

3. Figure With a Combination of Color and Line Styles

The figure now incorporates both adequate color contrast and line styles. Lines styles should not replace proper color contrast but can be used in addition to proper color contrast to further enhance accessibility. Panel E shows how the figure would look to someone with normal color vision. Panel F shows what Panel E would look like to a person with color-deficient vision. Although the color contrast alone is adequate to make the figure accessible, the distinct line styles make the figure even more accessible. 

Figure 3

Student Happiness Ratings as a Function of Year and Country of Origin

4. Figure With Labeled Lines Instead of a Legend

The figure now has labels next to the lines instead of in a legend. Panel G shows how the figure would look to someone with normal color vision. Panel H shows what Panel G would look like to a person with color-deficient vision. Labels are helpful for people with cognitive disabilities and those with low vision who may zoom in on the graphic and might have difficulty associating the legend labels with the lines. Labels can also be used in conjunction with a legend depending on available space. Labels do not replace proper color contrast or line styles but can provide even more accessibility. 

Figure 4

Student Happiness Ratings as a Function of Year and Country of Origin