Colour Vision Simulator
Around one man in twelve has some form of colour vision deficiency, and the most common effect is that reds and greens converge. A palette that looks obviously varied to you can collapse into two or three shades for them. This takes a palette, shows it as it would appear, and lists the pairs that were clearly different before and are nearly identical afterwards.
What this generator does
Converts each colour into the light values a display actually emits, applies the standard simulation for the chosen type of colour vision deficiency, and converts back. It then compares every pair of swatches before and after, listing those that were clearly distinct and end up close together.
How to use this tool
- Choose which type of colour vision to simulate and how many swatches to test.
- Compare each colour with its simulated version side by side.
- Read the list of pairs that become hard to tell apart.
- For any pair listed, add a second cue — a label, a shape, a pattern — rather than relying on colour.
Understanding the controls
- Type
- Deuteranopia and protanopia both affect the red-green axis and are by far the most common; tritanopia affects blue and yellow and is very rare.
- How many swatches
- Between 3 and 10 colours drawn from a varied palette, so there are enough pairs for collisions to show up.
- Seed
- Any word reproduces exactly the same set of swatches, so the same comparison can be shared or revisited.
Common use cases
- Checking whether a chart or status palette survives colour vision deficiency
- Designing indicators that do not rely on red against green
- Teaching why colour alone should never carry meaning
- Reviewing a brand palette for accessibility before it is settled
- Generating a reproducible set of swatches from a seed
How this generator works
The simulation works on light rather than on the encoded colour values, so each colour is first linearised before the transformation and re-encoded afterwards. The result has a property worth knowing: applying it twice changes nothing the second time, because the colours are already inside the reduced range. Greys come through untouched, since a colour with no hue has nothing to lose — both facts are confirmed every time before anything is shown.
Randomness and fairness
The palette is drawn at random from a fixed set of varied colours; the simulation itself is a deterministic transformation. A seed reproduces the same swatches exactly and is therefore explicitly not cryptographically secure. Without a seed the browser's cryptographically secure generator is used.
For how randomness is produced across the whole site, see how Generate Random works.
Limitations and good to know
- Simulates dichromacy — a missing cone type. Anomalous trichromacy, where a cone is shifted rather than absent, is far more common and is not modelled.
- An approximation. It is a guide for design decisions, not a substitute for testing with people who actually have colour vision deficiency.
- Swatches come from a fixed palette rather than accepting your own colours.
- Screen calibration, ambient light and display gamut all change what anyone sees, and none of that is accounted for.
- Palettes are not stored between visits; seed one you want again.
Privacy and your data
Every colour is converted in your browser. Nothing about the palette or your seed is transmitted or kept.
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