Color Contrast Requirements for Accessible PDFs

Low-contrast text — light gray on white, a pale color on a tinted background — is hard to read for people with low vision, color vision deficiencies, or anyone on a dim screen in bright light. WCAG sets concrete minimum contrast ratios that PDFs must meet.

The contrast ratios

• Body text needs a contrast ratio of at least 4.5:1 against its background.
• Large text (about 18pt, or 14pt bold) needs at least 3:1.
• These are the WCAG 2.1 Level AA thresholds that Section 508 and most laws reference.

Color is not the only signal

Never use color alone to convey meaning. "Items in red are overdue" fails for users who cannot distinguish the color. Add a label, icon, or text marker as well.

How to check and fix contrast

1. 1Use a contrast checker with the foreground and background color values to get the ratio.
2. 2For failing text, darken the text or lighten the background until it meets the threshold.
3. 3Pay attention to text over images or gradients, where contrast varies across the text.
4. 4Re-export from the source once the colors are corrected.

Contrast is partly a judgment call on complex graphics, so combine an automated check with a visual review. Run a free check here to flag the obvious failures first.