Colour blindness simulator
Enter two colours to see them through eight types of colour vision, and find out whether they stay apart. Everything runs in your browser.
Colour A on the left, colour B on the right. Click a value to copy it.
How each type sees them
The colour difference (ΔE) between the pair, per type. Smaller means harder to tell apart. We treat 25 and above as distinct and under 10 as nearly identical — a practical threshold on CIE76, not a standard.
No long-wavelength (red) cones. Reds look dark and blend into greens.
Shifted red cone sensitivity, so red and green separate less clearly.
No medium-wavelength (green) cones. Red and green are hard to separate.
The most common type. Red-green separation weakens while lightness differences survive.
No short-wavelength (blue) cones. Blue blends into green, yellow into pink.
Reduced blue cone sensitivity, so blue and yellow separate less clearly.
No colour discrimination at all — only lightness.
Colours appear heavily washed out.
CSS colour names that collapse together
Pairs that are clearly different to typical colour vision but converge under deuteranopia. If you use two of these together, separate them by lightness or shape as well.
| Pair | Typical ΔE | Deuteranopia ΔE |
|---|---|---|
| Limegreen +Tomato | 126.3 |
5.8 |
| Crimson +Forestgreen | 121.1 |
3.0 |
| Crimson +Green | 123.7 |
8.9 |
| Deepskyblue +Fuchsia | 118.0 |
8.5 |
| Deepskyblue +Magenta | 118.0 |
8.5 |
| Coral +Limegreen | 113.5 |
4.4 |
| Firebrick +Green | 108.5 |
2.9 |
| Lime +Orange | 110.9 |
7.8 |
| Lightsalmon +Springgreen | 110.0 |
9.3 |
| Firebrick +Forestgreen | 106.4 |
6.3 |
How the simulation works
Dichromacy uses Brettel, Viénot and Mollon (1997): the colour moves into LMS space and is projected onto the nearer of two half-planes along the missing cone axis. The popular single-plane shortcut is not used here because it leaves blue almost untouched under tritanopia.
Anomalous trichromacy (the “-anomaly” types) is approximated by mixing typical vision with the dichromatic result. Real severity varies a great deal from person to person.
⚠️ A simulation is a checking tool, not a window into someone else’s vision. Read it as “this pairing may be risky”, and design so that colour is never the only carrier of meaning — pair it with shape, labels or patterns.
Frequently asked questions
How common is colour vision deficiency?
Roughly 8% of men and 0.5% of women of Northern European descent, varying by population. Most of it is red-green, and deuteranomaly is the most common single type. Blue-yellow deficiency and achromatopsia are far rarer.
Is changing colours enough to be accessible?
No. WCAG 1.4.1 asks that colour never be the only way information is conveyed. Add shapes or patterns to chart series, underline links, and label states with an icon or word. Contrast is a separate check.