She is..... WAS part of an organization called "Black Rose", like a weird shadow society in Noxus or something among the lines. The Black Rose title does not apply to her person directly. "Amongst the cults, covens, and secret societies that call this labyrinth their home, LeBlanc, the Deceiver, presides over the Black Rose". [link] (you can read the whole story there). So that's probably why she doesn't have a black rose themed skin.
I could go on and on why this picture doesn't really fit her personality or character (to me it feels like this is a whole different person), but I'm not here to nitpick. Brilliant drawing, how ever. I envy your skills and creativity.