Watercolour appears lighter than expected after drying. What should be considered during practice?

Correct answer: Test the drying-lightening effect with a sample

The governing concept is the difference between wet and dry colour appearance in watercolour. Watercolour washes often look somewhat darker while wet and lighter after water evaporates, so a practice swatch should be allowed to dry before judging its final value. Adding black to every colour distorts hue, permanently wet paper is impractical, and excessive thickness can damage the wash or paper.