Which condition is most suitable for making a clean orange colour?

Correct answer: Mix red and yellow with a clean brush

In traditional paint mixing, orange is a secondary colour produced by combining the primary colours red and yellow. A clean brush prevents traces of blue or other pigments from contaminating the mixture and making it dull or muddy. Blue and yellow produce green, red and blue produce violet, and mixing all three usually reduces clarity. Therefore, option C is the most suitable condition.