Hello,
Whatever we try we were unable to set a [tabless] tabpanel to be transparent.
(We use it to have contextual icon bars in custom controller, with transparent buttons on a texture[imagemedia])
Using 2.1.1 rc1 on Windows XP and OsX.
The tabpanel object IS transparent! The thing that isn’t transparent is the BODY of the form showing up in the tabpanel. There’s no way to do what you want currently - unless you put the slice of the image into the BODY of the form showing in the tabpanel.
This confirm my opinion I will use Bob’s slicing option as soon as graphic interface will be definitive in our project. As I will have a lot of specific tabs in the custom controller.
… and sorry for this late answer, but I was not in my office last week.