Heya Chilli,
Unless Superfly or someone comes on and says otherwise, then to my knowledge, no opacity within the graphic itself other than the transparent (176,176,176) background color. The reason I say this is because native transparency (or alpha transparency) cannot be written within a bitmap format. There are formats that do support it (.gif, .png) but not bitmap. Bitmap extensions automatically assign white to any portion of a graphic you would have (alpha'd) transparent.
So in a nutshell. IMO, unless HTC accepted .gifs or .pngs, no opacity changes in the graphic can be reflected in the game. Thats why HTC gave us 176 in the beginning.
ReDhAwK