Choosing accessible colour contrast

All colour combinations must have sufficient contrast.

headings must have a colour contrast of at least 3:1
body text must have a colour contrast of at least 4:5:1
very high contrast, like pure black text on a white background, can be hard to read and cause eye strain
avoid placing text over images or textured background - if you must place a solid or a transparent dark background behind the text (assuming the text is in white or other light colours)

Use tools to check colour combinations

WebAim’s contrast checker tells you if your combinations pass or fail the web content accessibility guidelines (WCAG) at AA and AAA
Who can use shows how your combinations look to people with certain eye conditions and in certain light settings
Accessible colours checks your contrasts and suggests alternate text or background colours that will pass WCAG AA and AAA

Results from WebAim’s contrast checker showing a colour combination with enough contrast to pass WCAG AA and AAA standards for normal text, large text and user interface components.

Results from Who can use test showing contrast ratio for a colour combination and if the combination will pass or fail WCAG standards for users with different visual conditions.

Results from Accessiblecolours.com showing that a suggested combination of colours will fail WCAG AA standard and suggesting similar text and background colours that will pass.