How to change the backgroundcolor of a combo Box button?

[Tiemo Hollmann TB]

Hello,

I would like to change the background color of a combo Box button, but don't
succeed. With all other button types (option, pulldown,.) the background
color changes. Same with the opaque property, so that I also can't set the
opaque to false and put a colored rectangle behind the button.

Is this a wanted behaviour or a bug? Any other proposals who to cange the
backgroundcolor of a combo Box?

Thank you

Tiemo (Win XP, Rev 3.0)