Why Simulating Color Blindness Matters for Real Accessibility Checks
Color blindness affects roughly 8% of men and 0.5% of women, predominantly forms affecting red-green distinction (protanopia, deuteranopia) — a large enough share of any real audience that "does this design rely on color alone to convey meaning" is a genuinely practical accessibility question, not an edge-case concern (see Complete Guide to Web Accessibility for the broader context this fits into).
Simulating these deficiencies works by applying color transformation matrices that approximate how each condition alters perceived color — protanopia and deuteranopia both primarily affect red-green discrimination (through different underlying mechanisms), tritanopia affects blue-yellow discrimination specifically (much rarer), and achromatopsia (full monochrome vision) removes color discrimination entirely, leaving only brightness contrast to convey any distinction.
Running this simulation against a real design or image immediately reveals whether critical information — a warning color, a status indicator, a chart's data series — becomes genuinely ambiguous or indistinguishable under a given deficiency, which is exactly the kind of problem that's very easy to miss when reviewing a design only with typical color vision, since the distinction that seems obvious to the reviewer may not exist at all for a meaningful share of actual users.