If a colour looks correct when wet but becomes too light after drying, what should be done next time?

Correct answer: Make the mixture slightly more saturated and test a dry sample

The governing concept is accounting for the wet-to-dry change in perceived colour. Since the dried result is too light, the next mixture should be made slightly more saturated or concentrated, and a small test area should be allowed to dry before the final application. More water or white would normally make the result lighter, while changing paper alone does not correct the mixture. Therefore, option D is correct.