How to Fix Color Contrast in a PDF
Standards this affects
- WCAG 2.1 — 1.4.3 Contrast (Minimum) (Level AA)
- Section 508 — 503 / WCAG 2.0 AA by reference
- PDF/UA — Supports WCAG; contrast is a visual-design requirement
What this means
Color contrast is the difference in luminance between text and its background. WCAG 2.1 AA requires a ratio of at least 4.5:1 for normal text and 3:1 for large text (roughly 18pt, or 14pt bold) and for meaningful graphics/UI components.
Why it matters
Low-contrast text — light gray on white, thin colored text on a tinted background — is hard or impossible to read for people with low vision, color vision deficiencies, or anyone in bright light. Contrast is a visual requirement, so unlike tagging it generally must be fixed in the source design.
How the checker flags it
- The checker or a manual review flags text below 4.5:1 (or 3:1 for large text).
- Light gray body text, or colored text on a colored background, that's hard to read.
- Information conveyed by color alone (also check WCAG 1.4.1).
How to fix it
- 1
Measure the contrast
Use a contrast checker (e.g. the WebAIM Contrast Checker) on the foreground and background colors. Aim for at least 4.5:1 for body text and 3:1 for large text and key graphics.
- 2
Fix it in the source document
Darken text or lighten backgrounds in the authoring app (Word, InDesign, PowerPoint), then re-export the PDF. Contrast can't be reliably fixed by tagging — it's about the colors themselves.
- 3
Don't rely on color alone
If color communicates meaning (e.g. red = error), add a text label or icon so the information survives for users who can't distinguish the colors.
- 4
Re-export and verify
Regenerate the PDF and re-measure the updated colors to confirm they meet the AA thresholds.
Check your PDF for this issue
Upload your PDF to see whether it has this problem — and every other PDF/UA and WCAG 2.1 AA issue. Free, instant, no signup required.
Frequently asked questions
- What contrast ratio do I need?
- WCAG 2.1 AA requires 4.5:1 for normal text, 3:1 for large text (about 18pt regular or 14pt bold), and 3:1 for meaningful graphical objects and UI components.