Is this possible with GTK?

[rainwalker]

Just an idea, but I think that it looks really nice when the color of a window blends into a somewhat transparent title bar, like the one in this screenshot.
Is it possible to create themes that would recognize what the color of the window's contents are, and then set the title bar to match that?

[theophile]

My understanding is that the gtk theme determines what the color of the windows contents is. Numerous wm themes inheret properties from the gtk these and there are many seemless wm themes.