Colour Blindness Simulator

How to use the colour blindness simulator

1. Pick two colours to compare, or choose an image.
2. Check whether they stay distinguishable in each row.
3. If a pair collapses, add a non-colour cue rather than changing the shade.

About this tool

Around one man in twelve has some form of colour vision deficiency, so a red-and-green status indicator is illegible to a substantial share of any audience. This shows what they see.

The colour-pair check is the more directly useful half. It reports how far apart two colours are and how far apart they remain under each deficiency, so you can see that a red error state and a green success state collapse from clearly different to nearly identical — the single most common accessibility failure in interface colour.

The simulation converts to linear RGB before projecting onto the plane the missing cone cannot distinguish, then converts back. That linearisation matters: applying the same matrices directly to gamma-encoded sRGB values, which many simple implementations do, produces visibly wrong colours.

One honest limit. These model dichromacy, where a cone type is entirely absent, and that is the severe form. Most affected people have anomalous trichromacy — the cone is present but shifted — so their experience sits between these images and the original. Treat the result as a worst case worth designing for rather than a literal rendering of anyone's vision.

The practical fix is almost never a different shade. It is to stop relying on colour alone: add an icon, a label or a pattern, so the information survives whatever the reader can see.

Common uses

• Checking whether a chart's colours are distinguishable.
• Testing status colours before shipping an interface.
• Reviewing a design for accessibility.

Frequently asked questions

Which type of colour blindness is most common?

Deuteranopia and its milder form, affecting red-green discrimination. Roughly one man in sixteen; far fewer women, because the genes involved are on the X chromosome.

Is this exactly what colour blind people see?

No. It models dichromacy, the severe form where a cone type is missing. Most affected people have a shifted cone rather than an absent one, so their experience is milder than this.

How do I fix a colour pair that collapses?

Usually not by changing the shade. Add a second cue — an icon, a label, a pattern, a difference in lightness — so the meaning does not depend on colour at all.

Is my image uploaded?

No. The simulation runs on your device through the canvas, so unreleased designs stay on your machine.