Checklist item: All information conveyed with color is also available without color.
Guideline: Ensure that text and graphics are understandable when viewed without color.
If color alone is used to convey information, users with devices that have non-color or non-visual displays will not receive the information. When foreground and background colors are too close to the same hue, they may not provide sufficient contrast when viewed using monochrome displays or by people with different types of color deficits.
To accommodate color-deficient users, designers should:
- Select color combinations that can be discriminated by users with color deficiencies;
- Use tools to see what Web pages will look like when seen by color deficient users;
- Ensure that the lightness contrast between foreground and background colors is high;
- Increase the lightness contrast between colors on either end of the spectrum (e.g., blues and reds); and
- Avoid combining light colors from either end of the spectrum with dark colors from the middle of the spectrum.
Example: There are two examples, each simulating how the form may appear to someone with color deficits. The first example is of a form that uses only color to indicate required fields. The second example was modified by adding a second indication of a required field. In this case, asterisks were used.
