Simulate the common forms of colour vision deficiency on a palette or on a screenshot. For a palette it also flags any two colours that are easy to tell apart normally and nearly identical to some learners, which is exactly what breaks a red and green right-and-wrong indicator.
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| Vision | #D22B2B | #2BA84A | #E8B400 | #2B6CD2 |
|---|---|---|---|---|
| Normal vision | ||||
| Deuteranopiaabout 1 in 16 men | ||||
| Protanopiaabout 1 in 100 men | ||||
| Tritanopiarare, and not sex-linked | ||||
| Achromatopsiavery rare |
These are distinct to most people and nearly identical to some. If either colour is carrying meaning on its own, that meaning is lost. Add a shape, an icon or a label so the colour is not the only signal.
Simulates deuteranopia, protanopia, tritanopia and complete colour blindness, either on a palette or on a screenshot. For a palette it also compares every pair and flags any two colours that are easy to tell apart normally and nearly identical under one of the simulations.
Seeing a slide in simulated colours is interesting. Knowing that your correct green and your incorrect red become the same colour for roughly one man in sixteen is actionable. If a colour is the only thing carrying a meaning, that meaning disappears for those learners, and the fix is to add a shape, an icon or a word rather than to change the colour.
The simulation uses the matrices from Machado, Oliveira and Fernandes, which is the model most accessibility tooling is built on. They are defined against linear light, so the colours are linearised before the matrix is applied and re-encoded afterwards. A lot of implementations skip that step and apply the matrix straight to the encoded values, which looks approximately right and is wrong by most in the mid-tones, which is exactly where course palettes sit.
It simulates the absence of a cone type, which is the severe form. Anomalous trichromacy, where a cone is shifted rather than missing, is far more common and milder. Treat a pass here as necessary rather than sufficient, and treat a failure as definite.