Understanding SC 1.4.1:Use of Color (Level A)

Intent

The intent of this Success Criterion is to ensure that all sighted users can access information that is conveyed by color differences, that is, by the use of color where each color has a meaning assigned to it. If the information is conveyed through color differences in an image (or other non-text format), the color may not be seen by users with color deficiencies. In this case, providing the information conveyed with color through another visual means ensures users who cannot see color can still perceive the information.

Color is an important asset in design of Web content, enhancing its aesthetic appeal, its usability, and its accessibility. However, some users have difficulty perceiving color. People with partial sight often experience limited color vision, and many older users do not see color well. In addition, people using limited-color or monochrome displays and browsers will be unable to access information that is presented only in color.

Examples of information conveyed by color differences: “required fields are red", “error is shown in red", and “Mary's sales are in red, Tom's are in blue". Examples of indications of an action include: using color to indicate that a link will open in a new window or that a database entry has been updated successfully. An example of prompting a response would be: using highlighting on form fields to indicate that a required field had been left blank.

This should not in any way discourage the use of color on a page, or even color coding if it is complemented by other visual indication.

If content is conveyed through the use of colors that differ not only in their hue, but that also have a significant difference in lightness, then this counts as an additional visual distinction, as long as the difference in relative luminance between the colors leads to a contrast ratio of 3:1 or greater. For example, a light green and a dark red differ both by color (hue) and by lightness, so they would pass if the contrast ratio is at least 3:1. Similarly, if content is distinguished by inverting an element's foreground and background colors, this would pass (again, assuming that the foreground and background colors have a sufficient contrast).

However, if content relies on the user's ability to accurately perceive or differentiate a particular color an additional visual indicator will be required regardless of the contrast ratio between those colors. For example, knowing whether an outline is green for valid or red for invalid.

This criterion does not directly address the needs of users with assistive technologies. It aims to ensure that sighted users who cannot distinguish between some colors can still understand content. How information is conveyed to assistive technology users is covered separately in other criteria, including (but not limited to) 1.1.1 Non-text Content, 1.3.1 Info and Relationships, and 4.1.2 Name, Role, Value.

Conversely, even if information that is conveyed by color differences is appropriately conveyed to assistive technologies, it does not necessarily pass this criterion, as sighted users who cannot distinguish between certain color may not necessarily be using any assistive technologies. This criterion requires a visible alternative to color.

Benefits

Users with partial sight often experience limited color vision.
Some older users may not be able to see color well.
Users who have color-blindness benefit when information conveyed by color is available in other visual ways.
People using limited color monochrome displays may be unable to access color-dependent information.
Users who have problems distinguishing between colors can look or listen for text cues.

Examples

A form that uses color and text to indicate required fields

A form contains both required and optional fields. Instructions at the top of the form explain that required fields are labeled with red text and also with an icon. Users who cannot perceive the difference between the optional field labels and the red labels for the required fields will still be able to see the icon next to the red labels.
An examination.

Students view an SVG image of a chemical compound and identify the chemical elements present based both on the colors used, as well as numbers next to each element. A legend shows the color and number for each type of element. Sighted users who cannot perceive all the color differences can still understand the image by relying on the numbers.

Related Resources

Resources are for information purposes only, no endorsement implied.

Techniques

Each numbered item in this section represents a technique or combination of techniques that the WCAG Working Group deems sufficient for meeting this Success Criterion. However, it is not necessary to use these particular techniques. For information on using other techniques, see Understanding Techniques for WCAG Success Criteria, particularly the "Other Techniques" section.

Sufficient Techniques

Select the situation below that matches your content. Each situation includes techniques or combinations of techniques that are known and documented to be sufficient for that situation.

Situation A: If the color of particular words, backgrounds, or other content is used to indicate information:

Situation B: If color is used within an image to convey information:

Advisory Techniques

Although not required for conformance, the following additional techniques should be considered in order to make content more accessible. Not all techniques can be used or would be effective in all situations.

Using CSS to change the presentation of a user interface component when it receives focus

Failures

The following are common mistakes that are considered failures of this Success Criterion by the WCAG Working Group.