What is most important for controlling colour spread in wet-on-wet technique?

Correct answer: Moisture of the paper and brush

The governing principle of wet-on-wet painting is that moisture controls the movement of diluted pigment. The wetness of the paper and the amount of water held by the brush determine how far and how quickly the colour spreads. Therefore, option A is correct. Paper colour, brush price, and the painting title have no direct effect on pigment flow or edge control.