People with color blindness often have difficulty distinguishing certain colors, such as red and green or blue and yellow. Almost 5% of the population and 8% of men have some form of colorblindness. When color combinations (such as red text on a green background) are of insufficient contrast, the words can actually disappear to a person with colorblindness. You can help prevent this by selecting strong, contrasting color combinations and by labeling things that are otherwise distinguished only by color on a page (think charts and graphs).
- Provide sufficient contrast for all text and for informational graphics such as charts.
The Gray Scale Test: Print your charts and other graphic in gray scale and give it to someone who knows nothing about the data. Can she read it with ease? Can she distinguish any parts that are not labeled? For example, can she match the colors in the legend to the colors in the chart? For testing text color on background, use this color contrast checker (you are aiming to pass "WCAG AA").
This example is easy to distinguish, but only if you can see the colors as intended:
- Don't use color as the only way to convey content. You should also use direct text labels or changes in shape or texture. In the following example, the graph has its parts directly labeled. It also uses texture instead of color, to distinguish its elements. You do not need to do both: