Which mixture is more likely to create a warm brown?

Correct answer: Add a little blue to red-orange

The governing concept is temperature-controlled colour mixing. Red-orange is a warm base, and adding only a small amount of blue, which is cooler and complementary to the warm family, reduces its brightness and moves it toward a warm brown. The warm base must remain dominant. Black with blue stays dark and cool, while white with green creates a lighter green; adding blue to violet makes the mixture cooler. Thus, option B is correct.