In this technique, you surround a figure with a complementary color or, in Seurat's painting, a lighter hue.

NPR: Using Science to Rescue Art

The biological basis for this complementary color effect is not well understood, nor is the depth of shadow, which is also an illusion.

CNN: What the brain draws from: Art and neuroscience

With red and white light, the shadow of the object appears in the complementary color -- cyan -- and the shadows change as your angle of vision changes.

CNN: What the brain draws from: Art and neuroscience

Although at first glance this flamboyant vase presents a seeming welter of surface ornament, on closer examination we see how Lycett, working within the principles of visual harmony and balance central to Aestheticism, deftly controls this abundance, deploying his ornamental motifs in a dramatic series of bands that alternate complementary textures and hues within a narrow but vivid color palette.

WSJ: Masterpiece: Gilded Abundance, Elegantly Restrained