How should yellow be added when muting bright violet?

Correct answer: In very small amounts gradually

The governing concept is complementary colour mixing: yellow and violet are opposite hues, so they reduce each other’s saturation. Because a complementary addition can change a bright mixture rapidly, yellow should be introduced in tiny amounts, with the result checked after each addition. Option C is correct. Equal or excessive quantities may produce a dull yellow-brown mixture, while black is unnecessary and can make correction harder.