If adding white reduces transparency in watercolour, what is a better way to obtain a lighter colour?

Correct answer: Use more water and the brightness of white paper

The governing watercolour principle is that value is usually lightened by dilution rather than by adding opaque pigment. More water spreads the existing pigment into a thinner, more transparent film, allowing the brightness of the white paper to reflect through it. Adding black darkens and dulls the colour, a complementary colour reduces saturation, and a thick layer increases coverage instead of transparency. Therefore, option A is the best method for obtaining a lighter transparent watercolour.