The main types
- Protanopia / protanomaly — reduced red sensitivity; reds look darker and can be confused with greens.
- Deuteranopia / deuteranomaly — reduced green sensitivity; the most common form, also confuses red and green.
- Tritanopia / tritanomaly — reduced blue sensitivity; blues and greens, or yellows and pinks, can merge.
- Achromatopsia — complete colour blindness; the world appears in greys.
Why it matters for design
If a chart uses only red and green, or a status dot relies on hue alone, a sizeable share of users cannot read it. Colour is a useful signal only when it is not the only signal.
- Add labels, patterns or shapes alongside colour.
- Keep text contrast high (4.5:1 for body text).
- Avoid red/green as the only distinction for success and failure.
How simulation works
A simulator applies the transform that a given deficiency imposes on colour, so you can see which distinctions disappear. It is an approximation of one person's vision, not a diagnostic test — but it reliably catches designs that depend on a single hue difference.
Frequently Asked Questions
Can colour blindness be cured?
No. It is usually inherited and permanent. Some special lenses change contrast for certain tasks, but they do not restore normal colour vision.
Is colour blindness more common in men?
Yes. The common red–green forms are carried on the X chromosome, so they affect roughly 1 in 12 men and 1 in 200 women.
How do I test my design?
Run the key screens through a simulator and check that no meaning depends on colour alone. Then verify contrast ratios for text.