Well, here we go. Is this all there is? Probably. But I think it can take us somewhere.
Now look at the colors in the shadows. That was one of the first things I learned from my painting instructor at the college where my wife taught. Before then, I’d never even noticed that shadows have color. In the example above, there’s a yellowish tinge across the bottom area of the top shadow (above the skull), probably reflected from the adobe-colored stucco. All those blues and purples, too. Some of that is from the sky. Hell, all of it, I guess.