Free tools / Contrast checker
Will people tell your series apart?
Check your palette before it ships.
Short answer
Chart marks need at least 3:1 contrast against the background (WCAG 2.1, 1.4.11), and enough difference from each other that people with colour-vision deficiency can still tell them apart. Paste your chart colours to check both, on a dark or a light background.
Updated Nov 2, 2026 · Example palette
Palette
Background
Simulate
2 issues
Series 3 is under 3 : 1 on dark. Series 1 and 2 look alike with deuteranopia.
Seen with deuteranopia
How it checks
3 : 1 against the background
Each colour against the canvas, as WCAG 2.1 asks for graphics (1.4.11 Non-text contrast). Text labels need 4.5 : 1.
Apart from each other
Every pair is compared with CIEDE2000 in the chosen view. Pairs closer than 10 are flagged: readers will mix them up.
Four ways of seeing
Protanopia, deuteranopia and tritanopia are simulated with the Machado 2009 model; greyscale shows the lightness alone.
Questions
What contrast do chart colours need?
At least 3 : 1 against the background for bars, lines and other marks (WCAG 2.1, 1.4.11). Labels and other text need 4.5 : 1.
Why check colour blindness?
About 1 in 12 men and 1 in 200 women have a red–green colour-vision deficiency. Two series that differ only in red and green can look the same to them.
What if two series look alike?
Change the lightness of one of them, not only the hue, or label the lines and bars directly so colour is not the only cue.
Can I check a light background?
Yes. Switch Background to Light: every ratio and every pair is checked again.
Other free tools
- Chart Chooser
- Free charts
- Glossary