"... twisting them up toward the frosted wedding-cake of the ceiling, and then rippled over the wine-colored rug, making a shadow on it as wind does on the sea."
More wind, water, and light. We've gotten used to it here in this windy, watery, light-and-dark world of the Gatsby project. This sentence seems like a made up imitation of a sentence from "The Great Gatsby," but I assure you it's there.
All that's happening here is a breeze blowing through the room, but we have a traffic jam of metaphor: flags, wedding-cake, and wine. What are we supposed to see here? And good lord, it's a room. Must we really believe that something cataclysmic is going on when a breeze blows the curtains? Maybe we should. Maybe all sorts of crazy stuff happens in a room and it is like an epic storm at sea.
The wine-colored rug stands in for the sea, so I have to assume that we're supposed to think of the "wine-dark sea" we hear about, repeatedly, in Homer's Iliad and Odyssey. It is an epic, contained in that room. The dark shadows ripple, turning the wine-rug into sea, so I guess the ceiling is the sky. I guess that's a fancy white ceiling with all sorts of fancy woodwork, resembling the ornamentation on a wedding cake. The curtains swirling around the wedding-cake textures are cloud-like, I suppose. So fabric and wood make the erstwhile cake-like ceiling into stormy sky and curtain-driven shadows make the otherwise wine-like carpet into roiling sea.
It's a tempestuous room, containing a marriage. Raise a toast and let's feed each other cake.