What is the best way to keep two colours clean in wet-on-wet technique?

Correct answer: Let them meet in a limited area without overbrushing

The governing concept is controlled wet-on-wet blending. Two fresh colours should be allowed to touch in a limited area so moisture creates a natural transition, while the brush makes only a few deliberate strokes. Continuous rubbing breaks the clean colour structure and can neutralise pigments into mud. Adding a third colour or black reduces clarity rather than preserving it. Thus option B is the best practice.