第一色覚異常（赤色盲）

Protanopia affects approximately 1% of males. People with this condition lack L-cone (long wavelength, red-sensitive) photoreceptors, causing red to appear very dark (nearly black at low brightness) and difficult to distinguish from green or brown. Unlike deuteranopia, protanopia significantly affects the perceived brightness of red, which can make red text or warning indicators less visible. Designers should ensure that red-coded information uses additional cues like icons, text labels, or patterns, and that red text has sufficient size and weight to remain readable.