Information is not conveyed by color alone.

This rule is to not refer to content or functionality solely by its color. For example, references to an internal or external link to the book which would be indicated by the color blue alone will not be readable by certain audiences.

Objectives

• Allow access to information for users whose terminal or reading software, technical assistance or disability (such as color blindness) do not allow them to visualize or differentiate colors
• Improve accessibility content for people with disabilities

Implementation

Provide a complement to the color to convey the information it carries. This complement, independent of the CSS formatting layer, can be of several types, for example:
• Provide semantic markup (strong, em, etc.);
• Add hatches, patterns, borders, etc. in maps and graphs.

Control

• The verification requires visually comparing two types of display of the book: a normal display and a display where the colors will be deactivated (rendered on a computer screen and rendered on an e-reader with a grayscale screen).
• The verification requires visually comparing two types of display of the book: a normal display and a display where the colors will be deactivated (rendered on a computer screen and rendered on an e-reader with a grayscale screen).

Validation

• Needs to be human verified.