A Treatise on Painting/Chapter 268
Chap. CCLXVIII.—Of Back-grounds suitable both to Shadows and Lights.
The shadows or lights which surround figures, or any other objects, will help the more to detach them the more they differ from the objects; that is, if a dark colour does not terminate upon another dark colour, but upon a very different one; as white, or partaking of white, but lowered, and approximated to the dark shade.