What is the best way to reduce saturation while keeping value correct in poster colour?
Correct answer: A
The governing concept is saturation control through complementary mixing. A tiny amount of the complementary colour neutralises some of the original hue and reduces its vividness; choosing a similar-value complement helps keep the lightness close to the required value. Therefore option A is correct. Much black lowers value, much white raises value, and sand is not an appropriate paint additive and would damage the mixture and surface.