If yellow poster colour is too intense but should not be made much darker, which colour is suitable in a tiny amount?

Correct answer: Violet

Violet lies opposite yellow on the traditional colour wheel, so it is yellow’s complementary colour. Adding a very small amount can neutralise or reduce yellow’s intensity without intentionally lowering its value as much as black would. B is correct, but the quantity must be tested carefully because too much violet will make the mixture muddy or shift it strongly toward a dull neutral. White lightens rather than neutralises it.