Colour Blindness Simulator

In short Around 8% of men and 0.5% of women have some form of colour vision deficiency, which in a typical audience means one in every twelve or so male visitors. The common forms affect red and green: deuteranopia and protanopia both collapse that axis, so red and green become hard or impossible to tell apart, while tritanopia affects blue and yellow and is far rarer. Achromatopsia, seeing no colour at all, is rarer still but is the strictest test — anything that survives it survives everything. The single rule that matters is that colour must never be the only carrier of meaning. A red invalid field and a green valid one are identical to a large minority of your users unless the red one also has an icon, a border change or a message. Charts that distinguish series by colour alone are the same failure at scale, and so are status dots. Simulating your palette is the fastest way to find these: if two swatches merge under deuteranopia, they cannot be the pair you use for pass and fail. Adding a shape, a label or a pattern fixes it permanently.