The impression I had the last time I used this feature wasn't that it used RGBA -- if that was all that it was, then I'd expect you'd be able to set a transparent background with a gconf value or something.
What I recall was that it would somehow grab the bitmap of the area behind the window, and then draw that partially transparent as part of its own background. The way you could tell this was happening was to use a asymmetric image (like, a flower or some landscape photo) and notice the background "sticking" as you drag the terminal window around.
What I recall was that it would somehow grab the bitmap of the area behind the window, and then draw that partially transparent as part of its own background. The way you could tell this was happening was to use a asymmetric image (like, a flower or some landscape photo) and notice the background "sticking" as you drag the terminal window around.