Color Blindness Simulator⭐ Special Tool

In-Depth Guide

Colour vision deficiency affects roughly 8 percent of males and 0.5 percent of females of Northern European descent per National Eye Institute data, and the impact varies by type: protanopia (absent L-cones), deuteranopia (absent M-cones), and tritanopia (absent S-cones) are the three dichromacies; protanomaly, deuteranomaly, and tritanomaly are the corresponding anomalous-trichromacy variants; monochromacy and achromatopsia are the rarer cone-absent total-colour-loss conditions covered by the Ishihara and HRR test plates. A simulator applies a mathematical transform, based on work by Brettel, Vienot, and Mollon (1997), to map a normal-vision image into the perceptual space of each deficiency type. FastTool's simulator runs the Brettel-Vienot-Mollon transforms client-side via WebGL shaders, so designers can drag any image or screenshot into the browser and see an instant side-by-side preview of eight deficiency profiles at once.

Why This Matters

WCAG 2.2 Success Criterion 1.4.1 requires that colour not be the sole means of conveying information in any interface. Testing a design against colour blindness surfaces failures early: a red / green status indicator that becomes indistinguishable under deuteranopia, a chart legend that collapses under protanopia, a form error state that relies on a red outline an anomalous trichromat cannot reliably see against the surrounding background. Catching these at design time costs a few minutes; catching them after launch triggers accessibility bug reports, compliance audits, and potentially Americans with Disabilities Act litigation risk for larger organisations.

Real-World Case Studies

• Dashboard chart redesign. A product designer building a financial dashboard tests her red-gain and green-loss table under deuteranopia and sees the two values look identical to that cone profile. She switches to a red and blue-cyan pair, adds arrow icons as a secondary signal, and a follow-up accessibility review passes without comment, preventing an issue that would have affected roughly one in twelve male users of the dashboard across the whole customer base in production.
• Map legend audit. A UX researcher on a public-transit app runs the app's route-density heat map through all eight deficiency simulations to catch colour-only information encoding. Under tritanopia the yellow high-density zone blurs into the green medium band, making the legend ambiguous. The team swaps to a viridis colour ramp, designed specifically to be perceptually uniform across colour deficiencies, and the map now reads cleanly for every profile tested without losing visual hierarchy.
• Brand identity stress test. A brand illustrator finalising a new logo checks the chosen red and forest-green pair against protanopia and deuteranopia before presenting to the client. The two colours collapse to near-identical olives under both deficiencies. She pushes the green toward a more cyan hue, keeping the brief's natural and earthy mood while restoring distinguishability, catching the problem before brand guidelines ship, not after an expensive rebrand cycle.

Technical Deep Dive

The Brettel-Vienot-Mollon 1997 algorithm operates in LMS (long, medium, short cone-response) colour space rather than the gamma-encoded sRGB we ship to displays. Convert sRGB to linear RGB (undo gamma approximately 2.2 via IEC 61966-2-1), then linear RGB to LMS via the Hunt-Pointer-Estevez matrix. For protanopia, project the LMS value onto the plane spanned by the neutral axis and the M-S plane, setting L to a linear combination of M and S that matches dichromat vision at each point. Deuteranopia and tritanopia apply analogous projections on different cone axes. Convert back to linear RGB, reapply gamma, render to the output canvas. Anomalous-trichromacy variants interpolate between the original and the dichromat projection by a severity factor (typical 0.5 to 0.7). Monochromacy applies a luminance-only transform using ITU-R BT.709 coefficients. Edge cases: the algorithm assumes sRGB primaries, so Display-P3 images must be converted first; HDR content is clamped to SDR before simulation; results are a perceptual approximation, not a physically accurate camera feed of a dichromat's eye.