Good visual contrast is essential for readability. It ensures that text and images are easily distinguishable from their background, which is particularly critical for users with visual impairments.

Objectives

• Ensure high readability for all content.
• Reduce cognitive load during reading.
• Improve content accessibility for people with disabilities.

Implementation

• Maintain a minimum contrast ratio of at least 3:1 between text and its background, as measured using the WCAG 2.0 algorithm.

Control

• During the design phase: Identify content where the contrast or brightness difference with the background might be insufficient. Use a tool such as the Colour Contrast Analyzer to calculate the ratio. Sample the foreground and background colors and verify that the resulting contrast ratio is 3:1 or higher.
• After production: Use the ACE (Accessibility Checker for EPUB) tool and review the report. Check the “Errors” tab for “color-contrast” issues. Follow the manual sampling procedure described above to verify any flagged items.