What should be corrected if two colours become completely muddy when a new colour is added to a wet layer?

Correct answer: Limit mixing and brush movement

The governing wet-on-wet concept is controlled interaction between moisture and pigment. Excessive stirring or repeated brushing breaks the colour boundaries, lifts pigment, and mixes opposites until the result loses clarity and becomes muddy. Option B is correct: use fewer strokes, control the water, and allow the colours to meet without overworking. More force or more paint worsens the problem, while scraping damages the surface.