Well, I changed my latest graphic a bit to try something out, and it appears that it doesn't matter, currently, if there is any transparency in the Carbonite logo graphic.
It may not be obvious, but most of it is transparent with only an "oval" of black behind the logo with the rest of it being transparent. When I click on the image for the larger view, the transparent part turns white, so if that is what you see, that's why. The uploaded image is a .png that is 512 x 256. No screen shot since it looks exactly like the previous one in-game.
I have another version I was going to try, also, but I think I'll wait for that one (or, more likely, not at all).
This one is black with the same oval behind the logo being transparent. It's even less obvious than the other one.