The three common types of colour vision difference, explained
Deutan and protan (red-green) are common; tritan (blue-yellow) is rare; complete colour blindness is rarer still.
Updated Sep 14, 2026 · by Marcus V., deutan, data-viz designer
Editor reviewed
The numbers
About 8% of men and 0.5% of women have a red-green colour vision difference. Deutan (green-weak or green-blind) is the most common, at around 6% of men; protan (red-weak or red-blind) about 2%. Tritan (blue-yellow) affects roughly 1 in 10,000 and is not sex-linked. Complete colour blindness (achromatopsia) is about 1 in 30,000.
What "weak" and "blind" mean
Anomalous trichromats (deuteranomaly, protanomaly) have three cone types but one is shifted; they see colour, with reduced separation between reds and greens. Dichromats (deuteranopia, protanopia) lack one cone type entirely.
What fails in products
Anything that encodes meaning with red vs green alone: status lights, charts, game tokens, cables, ripeness of fruit. The fix is redundancy — shape, label or pattern beside colour — which is what this club scores products on.
Language
We say "colour vision difference" or name the type. We use "colour vision deficiency" only where a source uses it, because it's a trait, not a defect.