What should be done on the palette to maintain the purity of primary colours?

Correct answer: Keep a separate clean area for each colour

Colour purity means preserving a colour’s original hue without accidental contamination. Keeping red, yellow and blue in separate clean palette spaces, and cleaning the brush before switching colours, prevents unwanted mixing. Therefore option B is correct. Mixing all colours would make a dull mixture, while removing water or keeping only black does not preserve the three primary colours.