It would be nice if interfaces supported PNG-Transparency for labels, buttons, and other controls that support images. Even if it was only Opaque vs. Transparent, without full alpha support, it would be a great help.

As it is now, if you want rounded corners or any non-box shape, you have to use colors that look sorta like parts of your background and hope they match up and look decent for half of your players. The only real substitute right now is abusing window transparency color, but that forces software rendering.