What is the method of working with a wet brush on wet colour called?

Correct answer: Wet-on-wet

The governing concept is the relationship between the moisture of the brush and the painted surface. Applying a wet brush or wet paint onto an already wet colour or surface is called the wet-on-wet method, so option A is correct. It allows colours to flow and edges to soften. Dry-on-dry is the contrasting method, while drawing and paper folding are unrelated activities.