Which colour is suitable for reducing the vividness of violet?

Correct answer: Yellow

The governing concept is complementary colour neutralisation. Yellow lies opposite violet on the traditional colour wheel, so a small amount of yellow reduces violet’s vividness or saturation. Blue and red are the primary colours used to form violet and usually reinforce its hue, while white lightens it into a tint rather than directly neutralising its complement. Therefore, option C is correct; too much yellow can make the mixture dull or muddy.