This translation has not been editorially reviewed yet. The German version is authoritative. Deutsche Fassung →
Accessibility
Why do error messages and links need more than just colour?
Error messages and links need more than just colour, because many people distinguish colours only to a limited extent — red-green colour blindness is the most common form. A required field outlined in red with no explanatory text stays invisibly marked for these visitors. Information must therefore be carried twice: colour plus text, icon, or underline.
Colour as an addition, never as the sole carrier
Three everyday cases show the problem. First, forms: if an incorrectly filled field is only outlined in red, a visitor with red-green colour blindness won't find the error — add a text message such as "Please enter a valid email address". Second, links in running text: if a link differs from the surrounding text only by its colour, many people won't recognise it as a link — underlining fixes that. Third, charts and status indicators: "green means available, red means fully booked" only works with an additional label or different icons. Colour remains explicitly permitted and useful — it just must never be the only source of information.
How our measurement engine checks the use of colour
The automated check with axe-core detects one typical partial case: links in running text that stand out from the surrounding text through colour alone — with no underline or sufficient brightness difference. Such cases flow into the report as a finding. The larger part of the criterion is beyond the reach of a machine: whether a chart is explained through colour alone, or whether an error message has a text in addition to the red outline, requires understanding the content. In line with our principle, an unremarkable pass therefore never automatically counts as proof — at the Gold Standard level, an auditor reviews forms, charts, and status indicators and makes the call.
- Check your forms: every error marker needs an explanatory text at the affected field, alongside the colour.
- Have links in running text underlined — colour alone makes them invisible to many visitors.
- Add labels or icons in charts and status indicators, in addition to the colour coding.
- View your page in greyscale once — every screen and many phones can do this — and check whether all the information is preserved.
- Mark required fields with the word "required" or an explained asterisk, never with colour alone.
FAQ
How many people are affected by colour blindness?
Red-green colour blindness is the most common form and mainly affects men. We deliberately don't give a percentage figure, since estimates vary depending on the source. What matters is: the group is large enough that purely colour-based marking regularly excludes visitors on any well-visited website.
Do I need to underline all the links on my website?
Links in running text, yes — there, underlining is the most reliable second signal alongside colour. In clearly recognisable navigation areas such as the main menu, the surrounding context itself counts as a signal, so no underline is needed there. The check with axe-core flags exactly the running-text links that stand out only through colour.
Can I keep using red and green for errors and success?
Yes — as long as the information is also present as text or an icon. A green success message with a checkmark and the sentence "Your inquiry has been sent" is accessible, because every visitor can read it. Colour alone, without text and an icon, is what excludes colour-blind people.