How should paint quantity be changed to show a background that is dark at the top and light at the bottom?

Correct answer: Reduce the paint and add a lighter mixture while moving downward

The governing concept is a gradual value transition. To move from a dark top to a light bottom, progressively reduce the amount of concentrated paint and introduce a lighter mixture as the brush moves downward. Therefore, option C is correct. Increasing paint or keeping a thick dark mixture prevents lightening, while unrelated colours break the unity of the background instead of producing a smooth gradient.