Which precaution is best for maintaining the purity of blue-violet?

Correct answer: Avoid contamination by yellow and orange

Maintaining colour purity means preventing unwanted pigments from lowering the colour’s saturation or shifting its hue. Yellow has a strong opposing relationship to blue-violet and can neutralise or dull it; orange can also push the mixture toward a warmer, less distinctly blue-violet appearance. Grey would intentionally reduce vividness, excessive water changes transparency rather than pigment purity, and a shared mixing area increases contamination. Hence, option B is the best precaution.