The colour filling became darker than required but the paint is still damp. Which correction is most appropriate?

Correct answer: Lift a limited amount of paint with a clean blotted brush

The governing technique is controlled lifting from a damp paint layer. A clean brush with most of its moisture blotted out can touch the dark area and absorb a small amount of pigment; repeated gentle touches give gradual correction. Adding dark paint worsens the value, hard rubbing can damage the surface, and washing the whole picture is excessive. Thus option D is the safest and most precise correction.