(who also said, "I work in whatever medium likes me at the moment." LOL!)
Can you tell I've got color on the brain? Ever since (well, and before) the NMBS color workshop, I've been seeing color theory in action everywhere. (Ok, so why is my blog BROWN? I even wore olive, khaki and black to the workshop!)
What Chagall is saying is, analogous colors -- "neighbors" that live beside each other on the color wheel -- are harmonious, and complementary colors (opposites on the color wheel) are "lovers" in the sense that they complete each other; that is, every pair of complementary colors contain a bit of all three primaries.
Internet resources have improved and multiplied thousand fold since I started doing color seminars for bead & fiber artists. Here's a great place that keeps getting better:
And wwwwow, here's another link I'd never seen before. It's called Color Vision and Art, "The Science of Vision and the Emergence of Art." Just go there. It's. . . well, vivid!