In addition to colour, use other ways to convey information

Colour can be used to accentuate or distinguish between different parts of content. For example, it can be used for a warning message on a page, or to distinguish between several lines in a chart. Efficient as it may be, it should not be used as the sole means of conveying information, indicating an action, provoking a response or distinguishing a visual element. Information that is only conveyed with color cannot be perceived (or not properly) by visitors who are color blind or visually impaired.

Also provide other ways like: text, text styles, icons, or patterns. For example, don’t just use a green or red dot, but a green check mark and a red cross. Or use not only a different color per line in a graph, but also place an icon on the line and provide a legend.