Colours & Contrast
Ensure sufficient contrast. Do not display important content using colour alone (e.g. colour legends for diagrams).
The requirements for the use of colour and contrast are the only aspects of accessibility that actually limit the visual creativity of designers to a certain extent.
Contrasts
It goes without saying that minimum requirements for the contrast ratio of text and background or of components such as form fields to the immediate surroundings are essential for people with visual impairments to use electronic media properly and efficiently. Too low a contrast is very difficult to compensate for even by means of user-?defined colour schemes.
Use of colour
Information must never be conveyed by colour alone. Think of a visual reservation system in which available seats and seats that are already taken are marked exclusively with green and red colours respectively. Colour-?blind people and others with visual impairments have great difficulty distinguishing between the categories.
Colours and contrast test procedure
Contrasts
- Search for content with low contrast ratios between text, form fields or graphic elements and their background.
- Measure the contrast ratio with the external page Colour Contrast Analyser tool and check the minimum value of 4.5:1.
Use of colour
Check illustrations and graphics in which data points are represented exclusively by colour assignment to a legend (typically in diagrams or reservation systems).