Color Blindness Sim

Preview an image under protanopia, deuteranopia and tritanopia. Free, runs entirely in your browser — no signup, and nothing you paste in is uploaded.

The three simulated types are missing or shifted cone responses: protanopia affects red cones, deuteranopia green, and tritanopia blue. Red-green deficiency is by far the most common, affecting roughly one in twelve men, which makes red-and-green status indicators one of the most reliably inaccessible patterns in interface design.

The design rule that follows is that colour must never be the only channel carrying meaning. Pair it with an icon, a label or a position, and the interface works for everyone. Simulation is the fastest way to see the failure, because a chart that is obvious to you can be genuinely unreadable to a colleague.