Guideline 1.4: Distinguishable - Make it easier for users to see and hear content including separating foreground from background.
Success Criterion 1.4.1: Use of Color - Color is not used as the only visual means of conveying information, indicating an action, prompting a response, or distinguishing a visual element.
Success Criterion 1.4.3: Contrast (Minimum) - The visual presentation of text and images of text has a contrast ratio of at least 4.5:1.
Success Criterion 1.4.5: Images of Text - If the technologies being used can achieve the visual presentation, text is used to convey information rather than images of text.
"While some guidelines are focused on making information available in a form that can be presented in alternate formats, this guideline is concerned with making the default presentation as easy to perceive as possible to people with disabilities. The primary focus is on making it easier for users to separate foreground information from the background. For visual presentations, this involves making sure that information presented on top of a background contrasts sufficiently with the background." [1]