Earth tones, which I really like, are good to use in contrast with color. In my composition below, the color represents one realm, while the muted colors inhabit the shadow world.

Action Wall Shadows
12″x9″ 140# Cold Pressed Watercolor Block

This makes me think of the cave painters who where lived in the real world, while their paintings were more or less monochrome, although I am still mystified about how they painted in the ambient darkness of cave light.  One can think of this painting as a projection of a vibrating object from outside Plato’s cave, whose dwellers only see the monochrome tones without benefit of any color at all.