It looks like the IT is handling the "home" portion of the desktop different than other areas of the desktop. The code for my task navigator panel sample produces a button with a transparent background without any problem. But the exact same code as a home applet (just changing hildondesktop.TaskNavigatorItem to hildondesktop.HomeItem) produces a button with a white background. I don't know why it's different, but we may have to figure that out to see if there's a way around it.