Different colour-deficiency types need different adjustments

What it is

Colour deficiency is not one condition but several: red-deficiency (protanopia / protanomaly), green-deficiency (deuteranopia / deuteranomaly, the most common), blue-yellow deficiency (tritanopia / tritanomaly, rare), and complete achromatopsia (very rare). A single "colour-blind mode" preset cannot serve them all—the red-green pair a deuteranope cannot distinguish is perfectly separable for a tritanope, whose blue-yellow problem the deuteranope does not share. A game with only one mode helps a substantial fraction of colour-deficient players not at all.

Why it happens

Different deficiency types lose resolution in different regions of colour space. Red-green deficiencies (roughly 5–8% of male population) lose resolution along the red-green axis while keeping blue-yellow; blue-yellow deficiency is the reverse. Adjustments that shift the whole hue space help no one—they simply move the collision from one region to another. Effective schemes optimise per type: verify the game's critical colour pairs (friend-or-foe, rarity, paths) under each target type's simulation and adjust pair by pair. This is also why redundant encoding (shape, pattern) is more robust than hue shifting—it does not depend on "choosing the right palette," a claim that is inherently type-sensitive.

Where it stops holding

Per-type modes carry the maintenance cost of multiple adjustment sets, and individual variation exists within each type (anomaly versus anopia severity), so presets remain approximations. "One mode for all" approaches validity under redundant encoding—shape encoding works for every deficiency type—which is why high-quality schemes are converging on "accessible by default + optional filters" rather than multiple hue-swap sets. Blue-yellow deficiency and achromatopsia affect very small populations, and a dedicated adjustment set for each has low marginal value; the sensible path to covering them is default redundant encoding rather than exclusive modes.

Applying it

• Offer at least "red-green deficiency," "blue-yellow deficiency," and optional "greyscale" filters—never a single colour-blind toggle.
• Audit critical colour pairs (friend-or-foe, rarity, paths, status colours) under each type's simulation filter, record the failing pairs per mode, and fix them within the corresponding mode.
• Verification: recruit testers with different deficiency types for their respective modes and measure judgement error rates per mode. An error rate that fails to drop significantly means that type's adjustment scheme is ineffective—return to the colour-pair level and redesign.

Related

• Same group: W8.03.1 Colour-blind modes must cover every colour-coded element · W8.03.2 Hue shifts alone are not enough—add shape or pattern redundancy · W8.03.4 Colour-only friend-or-foe identification creates real fairness problems
• Nearby: J2.03 Colour accessibility · C2.06 Colour perception · F2.02 Colour systems
• Search terms: protanopia · deuteranopia · tritanopia · colour deficiency types