Contrast (Enhanced)

Understanding WCAG2.0

Strict criteria for 1.4.3. In 1.4.3 I was requesting a 3:1 contrast ratio, but even bigger letters require a contrast ratio of 4.5:1.

Principle	Perceivable	Information and user interface components must be presentable to users in ways they can perceive.
Guideline	Distinguishable	Make it easier for users to see and hear content including separating foreground from background.
Criterion	Contrast (Enhanced) (1.4.6 AAA)	For visual presentation of text and character images, there is a contrast ratio of at least 7: 1.

URL of Techniques for WCAG 2.0

• G17: Ensuring that a contrast ratio of at least 7:1 exists between text (and images of text) and background behind the text
• G18: Ensuring that a contrast ratio of at least 4.5:1 exists between text (and images of text) and background behind the text
• G148: Not specifying background color, not specifying text color, and not using technology features that change those defaults
• G156: Using a technology that has commonly-available user agents that can change the foreground and background of blocks of text
• G174: Providing a control with a sufficient contrast ratio that allows users to switch to a presentation that uses sufficient contrast
• F24: Failure of Success Criterion 1.4.3, 1.4.6 and 1.4.8 due to specifying foreground colors without specifying background colors or vice versa
• F83: Failure of Success Criterion 1.4.3 and 1.4.6 due to using background images that do not provide sufficient contrast with foreground text (or images of text)