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Rule n° 176 - Information is not conveyed by color alone.

This rule consists of not referring to a content or function by its colour alone. For example, the mandatory nature of a form field marked in red may not be perceivable by everyone.

#Accessibility #Presentation #Conception


  • Give users whose browser, platform, technical aid or disability (like color-blindness) prevents them from viewing or differentiating between colors
  • Make the information accessible by web crawlers.
  • Improve the accessibility of content for people with disabilities.


In addition to colour, provide an additional mechanism to convey the information provided by the colour. This mechanism, independent of the CSS formatting layer, can be of several types:

  • provide semantic markup (strong, em, etc.);
  • add text indications (asterisk indicating a mandatory field);
  • add hatching, patterns, borders, etc. in maps and



Checking requires visually comparing two versions of the page: the normal version and a version where the colours are disabled. It is therefore easier to work with two screens. For each page checked:

  • Disable colour support via your test toolbar then switch the images to grayscale.
  • Check by comparing the two versions whether the version without colours shows any loss of information. This will be the case, for example, in a navigation menu where the current heading is only differentiated by its colour, or even in a map whose areas are simple solid areas of colour without borders or patterns.

Attention: Information may sometimes be independent of the colour in a title attribute, causing a tooltip to appear when hovering over the content. Because access to the tooltip from the keyboard is not currently possible by default in all browsers, this solution must be ruled out.

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