Skin discoloration
Spock with discolored skin
Skin discoloration was a change in the color of one's skin or skin pigmentation. Increased blood flow to the skin caused one to become flushed or blush, while decreased blood flow caused pallor.
Temporary skin discoloration was one side effect of melenex. In 2269, Doctor Leonard McCoy suggested that this symptom and brief unconsciousness would look bad enough to the Shore Leave Planet's master computer for it to whisk a melenex-dosed patient to its medical unit. (TAS: "Once Upon a Planet")
The auroral plague also caused changes in skin color related to the color of the aurora. (TAS: "Albatross")