Roughly 1 in 12 men and 1 in 200 women see color differently. Here is any picture twice — the way it is, and the way it lands for them. Point at a pixel to read both colors.
Move the pointer over either picture to sample a pixel, or focus one and use ←↑↓→ (Shift for bigger steps). Drop an image file anywhere on this panel to use your own.
pixel x 0, y 0
The image’s most-used colorful shades, all clearly distinct to start. The four tightest pairs after simulation: under ΔE 25 they are risky — still different, but not a difference you can count on. Under ΔE 12 they have merged into one color.
Applied in linear-light RGB. Full-severity matrices from Machado, Oliveira & Fernandes (2009); below 100% this blends linearly toward the identity matrix, which approximates their per-severity tables. Gray simulation uses CIE luminance weights. Distances are CIE76 ΔE in Lab.