PDF accessibility: colour blindness, contrast and screen readers

2 min read·25 July 2026

Approximately 8% of men and 0.5% of women have some form of colour blindness. Documents that rely too heavily on colour are unreadable for them. Learn how to make PDF files more accessible for people with visual impairments.

Common forms of colour blindness

Red-green colour blindness (deuteranopia and protanopia) is the most common form — people cannot easily distinguish red from green. Blue-yellow colour blindness (tritanopia) is rarer. Complete achromatopsia (total colour blindness) is extremely rare. Design for red-green as your baseline.

Increasing contrast

WCAG 2.1 requires a minimum contrast ratio of 4.5:1 for normal text and 3:1 for large text (18pt+). Black text on white has a ratio of 21:1 — ideal. Light grey on white (widely used in modern designs) often fails this threshold. Use PDFrust's greyscale function to see how your document looks for colour blind readers.

PDF grayscale

Try for free — no account needed

Try it now →

Never use colour as the only information carrier

Use colour only as a supplementary indicator — never as the only way to convey information. Bad: "the red items are urgent". Good: "the items marked with an exclamation mark (!) are urgent". Always add patterns, labels or shapes alongside colour in charts and tables.

Alternative text for images

Screen readers (software for blind and visually impaired people) read alt text aloud for images. Make sure all informative images in the PDF have a descriptive alt text. Decorative images get an empty alt text. This is also required for PDF-A/UA (the accessibility standard).

PDF tags for document structure

A tagged PDF has a logical document structure that screen readers can follow: headings (H1, H2), lists, tables and paragraphs. Without tags, a screen reader reads the text in random order. Check whether your PDF is tagged via PDFrust's file info tool.

Applying colour blind simulation

Temporarily convert your PDF to greyscale with PDFrust — if the information is still readable, the document is also suitable for people with colour blindness. Online tools such as Color Oracle or Adobe Acrobat's accessibility check can provide a more thorough simulation.