What precaution should be taken in watercolour to maintain transparency in a mixed colour?

Correct answer: Apply thin layers of colour

The governing principle of transparent watercolour is allowing light to pass through the pigment and reflect from the paper. Applying a thin, sufficiently diluted layer preserves this luminous effect, so option A is correct. Thick paint, heavy black, or poster white adds opacity and can cover the paper’s reflective surface, making the mixture look duller and less transparent.