The Core Requirement: Categorical Distinctness
Wayfinding color systems must achieve categorical distinctness — every coded category must be unambiguously different from every other coded category under real-world viewing conditions. Real-world conditions include variable lighting (fluorescent, LED, daylight), peripheral vision (signs read while walking, not studied), distance viewing, and color vision deficiency. These constraints drive wayfinding color selection toward a methodology similar to data visualization: choose hues that are maximally spaced around the hue wheel, ensure sufficient lightness difference between similar hues, and avoid placing red and green as the sole differentiators between categories.
