What should be done to mute red-orange without turning it brown?

Correct answer: Add a very small amount of blue

The governing concept is controlled neutralisation using a near-complementary colour. Blue is opposite the orange component of red-orange, so a very small amount can reduce vividness and mute the colour. Option A is correct because the quantity is limited. A large amount of blue or black can make the mixture muddy or brownish and lower its value sharply; much green can also neutralise the colour unpredictably rather than producing a clean muted red-orange. Add and test the blue gradually.