Which mixture is more likely to produce a warm grey?

Correct answer: Black and white with a little red or yellow

The governing concept is colour temperature in a neutral mixture. Black and white establish a grey base, and a small amount of red or yellow gives that base a warm undertone; hence option B is correct. A little blue generally shifts grey toward a cool temperature, while a large amount of green makes the mixture noticeably coloured rather than a warm neutral. Pure black is not grey because it has no white added. The modifier must remain small so the result still reads as grey.