What is the most controlled way to reduce excessive redness in a skin tone mixture?

Correct answer: Add a very small amount of green

The governing principle is complementary colour control: green is opposite red on the colour wheel. Adding green in a very small amount can neutralise some excessive redness without immediately making the skin tone extremely dark. Thus option A is correct. More red increases the problem, orange usually preserves or strengthens warmth, and only black reduces value harshly rather than balancing the hue.