PDF How To: Ensure Color Contrast

Why do I need to check the color contrast?

Checking color contrast ensures that text is readable for people with low vision or color blindness. It helps meet WCAG requirements and improves overall accessibility and usability for all users.

WCAG AA Contrast Ratios

In order to make PDFs accessible for low vision readers, a certain amount of contrast is required.

For normal text WCAG requires contrast ratios of 4.5:1 (AA) or 7:1 (AAA).
For large text WCAG requires contrast ratios of 3:1 (AA) or 4.5:1 (AAA).

Testing Color Contrast

Silktide automatically checks PDF color contrast on websites, but Adobe Acrobat requires manual testing. You can test contrast using a variety of tools by opening the PDF in Adobe Acrobat Pro or in a web browser.

Silktide Accessibility Toolbar: Includes a contrast checker with an eyedropper tool for WCAG compliance testing.
WebAIM Contrast Checker: Browser-based tool with a color picker for testing text/background contrast.
Colour Contrast Analyzer (CCA): Free tool for Windows and macOS.

Source Files

It’s best to make your original source file (e.g., Word, InDesign) accessible before converting it to a PDF. Editing the source file first is usually the easiest and most reliable way to ensure the final PDF is accessible.

View how to add titles to source files.

Word

Use the Accessibility checker to find hard to read contrast under Review > Check Accessibility.

InDesign

Use high-contrast color combinations when designing content.
Visually inspect text against backgrounds to ensure legibility.
Export a PDF and test using:
- Adobe Acrobat Pro’s high contrast preview settings
- Use external tools; Silktide, WebAIM or CCA for exact ratio checks

Use High Contrast Colors in Acrobat

Under Preferences, select Accessibility.
Select Replace Document Colors.
Select Use High Contrast Colors.
Select Change the color of line art as well as text.
Select OK.