This translation has not been editorially reviewed yet. The German version is authoritative. Deutsche Fassung
Accessibility
When is a contrast of 4.5:1 no longer enough?
Level AA requires a contrast of 4.5:1 to the background for text. For people with significant visual impairment, such as cataracts or age-related macular degeneration, this is at the limit. Level AAA criterion 1.4.6 raises the threshold to 7:1 for normal text and 4.5:1 for large text. The value is measurable, the implementation is a question of color choice.
What the Criterion Requires
Text and images of text achieve a contrast of at least 7:1 to the background. Large text, i.e. from 24 pixels normal or from 19 pixels bold, needs at least 4.5:1. Excluded are logos, purely decorative text and deactivated controls. The contrast shall be calculated from the luminances of the two colours using the formula of the WCAG; Black on white reaches 21:1, a medium gray on white often remains below 4:1.
What 7:1 Means in Colors
Dark writing on a bright background reaches 7:1 with shades of gray starting at around #595959 on white; Colored texts must be significantly darker than at level AA. Bright font on a dark background works with white on tones starting at around #4d4d4d. Many brand colors in medium blue, green or orange reach 7:1 only as a surface with white font, not as a font on white. A contrast mode that visitors can turn on is a permissible way if it captures all text.
This is how we deal with it
Today, the measuring core measures each text against the threshold 4.5:1 of level AA and indicates the measured value per reference point. The same measurement thus provides which texts reach 7:1 and which do not. The criterion is one of the few of the level AAA that are fully automatically decidable. It belongs to the category AAA in knowledge; The report contains the measured value.
Examples
Text with 4.5:1 instead of 7:1
body { color: #767676; background: #ffffff; } /* 4,5:1 – Stufe AA */body { color: #595959; background: #ffffff; } /* 7,0:1 – Stufe AAA */For normal text 7:1, for large text from 24 pixels 4.5:1. The measured value is for each reference in the report.
- Measure your text and background colors with a contrast calculator; Note the value for each pair.
- Darken flow text to at least 7:1; Headings from 24 pixels may remain at 4.5:1.
- Apply brand colors that do not reach 7:1 as font as areas with white font.
- Offer a mode of increased contrast if you do not want to change the brand in the standard, and check it on all sides.
