Which adjustment is suitable next time if a sample dries much lighter than expected?

Correct answer: Prepare the wet mixture slightly darker

Watercolour is usually applied transparently, and evaporation can make a dried passage appear lighter than it looked while wet. The correct adjustment is therefore to prepare the next wet mixture slightly darker, then test it again on a separate swatch. Option B compensates for the observed drying shift without changing the medium. More water would usually make the result lighter, white reduces transparency, and a dry brush does not solve value prediction.