Web pages shall be designed so that all information conveyed with color is also available without color, for example from context or markup. Ensure that a luminosity contrast ratio of at least 5:1 exists between foreground content and background.
Note: In the Manual Check page, you will find additional information on how to test for color.
Why is this provision necessary?
When colors are used as the sole method for identifying screen elements or controls, persons who are color blind as well as those people who are blind or have low vision may find the web page unusable.
Does this mean that all pages have to be displayed in black and white?
No, this provision does not prohibit the use of color to enhance identification of important features. It does, however, require that some other method of identification, such as text labels, must be combined with the use of color. This provision addresses not only the problem of using color to indicate emphasized text, but also the use of color to indicate an action. For example, a web page that directs a user to "press the green button to start" should also identify the green button in some other fashion than simply by color.