Plain Language Recommendations
Text, images of text, charts, or graphs must have a contrast ratio of at least 4.5:1. Large text (over 18 point or 14 point bold) must have a contrast ratio of at least 3:1. (Logos and decorative text not included.)
WCAG 2.0 Recommendations
Guideline 1.4: Distinguishable
Make it easier for users to see and hear content including separating foreground from background.