The contrast ratio of text to background color must be 4.5 or more to meet WCAG guidelines. You can check color combinations with these tools: [http://leaverou.github.io/contrast-ratio/ Contrast Checker] or [https://webaim.org/resources/contrastchecker/ WebAIM's Contrast Checker]
[[File:A11y-contrast.png|thumb|none|alt=Screenshot of color combinations with contrast ratios|400px|Contrast ratio of text over different backgrounds and the WCAG requirements]]
Be extra careful if you are placing text over an image as the same rules apply. System colors can be modified by changing the [[Branding|branding]].