What is necessary to maintain the brightness of watercolours?

Correct answer: Clean water and a clean palette

The governing principle is to prevent unwanted pigment contamination. Clean water and a clean palette keep colours separate and help transparent washes retain their brightness and clarity, so option A is correct. A dirty brush carries previous pigments into the next colour, while mixing every colour or adding black indiscriminately often produces dull, muddy mixtures. Rinse the brush between colours, remove excess residue, and replace visibly dirty water during the painting process.