The lower colour is showing through a light poster-colour layer. What should be done?

Correct answer: Apply a controlled opaque layer and add another thin layer after drying

The governing concept is coverage through controlled opaque layering. A light pigment often needs a sufficiently concentrated coat to hide a darker underlayer, but applying one thick coat can cause runs, lumps, or lifting. Option A is correct: apply an even opaque layer, allow it to dry, and add a second thin coat if needed. More water increases transparency, hard rubbing disturbs the wet film, and darkening the lower colour worsens the contrast.