What is a possible reason for orange becoming muddy?

Correct answer: Accidental mixing with blue

Orange is formed by mixing red and yellow. Blue is opposite orange on the traditional colour wheel, so accidental blue contamination can reduce orange’s saturation and make it look dull, greyish, or muddy. Clean red and yellow, a clean brush, and separate palette spaces support a clear orange instead. Therefore option A is correct. The governing concept is that unintended mixing with a contrasting or complementary colour lowers the visual intensity of the original mixture.