Color Blindness
How color-vision deficiency works and how to design palettes that survive it.
Color-vision deficiency affects roughly 1 in 12 men and 1 in 200 women - in a product with a million users, that is tens of thousands of people. Almost none of them see “in black and white”; they see a full world of color in which certain pairs collapse together. Design for the collapse, not for grayscale.
What actually differs#
Recall the cone diagram from the Introduction: normal color vision compares signals from three cone types, and the L and M curves already overlap heavily. In the common deficiencies, one cone type is either missing (-opia) or shifted toward its neighbour (-anomaly). Either way, the difference signal between L and M shrinks - and with it the ability to separate reds from greens.
Because most CVD is carried on the X chromosome, it is far more common in men. It is a spectrum: a mild deuteranomalous viewer may only struggle with muted colors in dim light, while a dichromat (missing the cone entirely) cannot distinguish saturated red from saturated green at all.
The types, by the numbers#
| Type | Affected cone | Prevalence (male) | Effect |
|---|---|---|---|
| Deuteranomaly | M shifted | ~5% | Most common form. Greens shift toward red; muted red/green/brown pairs blur. |
| Protanomaly | L shifted | ~1.3% | Reds look darker and duller; red/black and red/brown confusions. |
| Deuteranopia | M missing | ~1.2% | Red-green channel gone; red, orange, yellow, green collapse to a yellow-brown axis. |
| Protanopia | L missing | ~1.3% | As above, plus reds appear much darker (a red 'Stop' can read as black). |
| Tritanopia / -anomaly | S missing / shifted | ~0.02% (both sexes) | Rare. Blue/green and yellow/violet confusions. |
| Achromatopsia | No functional cones | ~0.003% | True absence of color vision, usually with light sensitivity. |
Which colors get confused#
For red-green CVD, colors that differ only in the red-green directionbecome metamers - they lie on the same “confusion line.” The classic traps:
- Red ↔ green (the famous one, worst when both are mid-dark)
- Orange ↔ yellow-green
- Brown ↔ dark red ↔ dark green
- Blue ↔ purple (purple's red component vanishes)
- Pink ↔ light gray
Designing palettes that survive#
- Vary lightness, not just hue. A palette whose steps differ in L stays distinguishable under every deficiency - lightness perception is intact in CVD. This is why OKLCH-built scales are inherently safer.
- Redundant encoding. Pair color with a second channel: icons on statuses, direct labels on chart series, patterns or dashes on lines. Color becomes reinforcement, not the message.
- Prefer blue-orange contrastsfor two-series charts - the axis best preserved across common deficiencies. The Okabe–Ito palette is a well-tested 8-color starting point.
- Simulate before shipping. Lumea's Color Blindness card renders your palette under protanopia, deuteranopia, tritanopia and achromatopsia using the standard Brettel/Viénot-style matrices - if two steps merge there, renumber your scale.