What should be done if a skin tone has the correct value but appears too grey?

Correct answer: Add a little suitable pure red or yellow

The governing concept is separating value from chroma. Since the value, or lightness, is already correct, the correction should add a small amount of a suitable warm hue without substantially changing lightness. A little pure red or yellow restores colour vitality and reduces the dull grey appearance. More grey, complementary colour, or black would generally make the mixture duller or darker and could disturb the correct value. Therefore, option A is the most controlled choice.