If watercolour appears too light after drying, what should be done next time?

Correct answer: Keep the wet mixture slightly more concentrated

The governing concept is the drying shift of transparent watercolour. Water evaporates as the wash dries, leaving a lighter-looking deposit than the wet mixture seemed to have. To compensate, the artist should prepare the next mixture with slightly more pigment or less water, while avoiding an excessively dark application. Therefore option C is correct. Adding more water would make the wash lighter, changing paper alone does not solve the value issue, and a dry brush is not the required adjustment.