About colour accessibility
Why contrast matters, who it helps, and what the standards mean.
What is colour contrast?
Colour contrast is the difference in perceived brightness between two colours. When text and its background have high contrast, the text is easier to read. When contrast is low, text can become difficult or impossible to read — even for people with typical vision.
Contrast is measured as a ratio. The minimum possible ratio is 1:1 (no contrast — identical colours) and the maximum is 21:1 (black on white or white on black).
Who benefits from accessible colours?
Accessible colour choices help far more people than you might expect:
- People with low vision — approximately 1 in 6 Australians experience some form of vision impairment.
- People with colour vision deficiency — around 8% of men and 0.5% of women have some form of colour blindness.
- Older adults — contrast sensitivity naturally decreases with age. By 60, most people need significantly more contrast than they did at 20.
- Anyone using a screen in bright sunlight — outdoor conditions can reduce effective contrast by up to 80%.
- People using low-quality or older screens — not everyone has a high-end display with accurate colour reproduction.
Understanding WCAG 2.1 levels
The Web Content Accessibility Guidelines (WCAG) 2.1 define two conformance levels for colour contrast:
| Level | Regular text | Large text |
|---|---|---|
| AA | 4.5:1 minimum | 3:1 minimum |
| AAA | 7:1 minimum | 4.5:1 minimum |
AA is the standard most organisations aim for. It provides a good level of accessibility for the majority of users and is the level typically required by accessibility legislation.
AAA is the highest level. It provides enhanced readability and is recommended for body text, long-form content, and critical information. Not all colour combinations can achieve AAA — it is a stretch goal rather than a blanket requirement.
Large text is defined as 18pt (24px) or above, or 14pt (approximately 18.66px) if bold. Large text has a lower contrast requirement because its size already makes it more readable.
Legal context
In Australia, the Disability Discrimination Act 1992 (DDA) requires that services — including websites — be accessible to people with disabilities. While the DDA does not specify WCAG compliance directly, WCAG 2.1 AA is the accepted benchmark referenced by the Australian Human Rights Commission.
Internationally, accessibility requirements are strengthening. The European Accessibility Act (effective 2025), the Americans with Disabilities Act (ADA), and similar legislation worldwide all point toward WCAG compliance as the standard.