Change NativeWindow background color

Hi, I'm developing ad Air application with Flash. This application creates other windows and plays video in fullscreen mode. Created windows have white background so in fullscreen mode i have white strips :-(
Do you know if is possible to change native window background color?
I can't create a transparent window because I load PDF documents with an HTMLLoader object in the same window.

Thanks
Francesca

Sorry for my terrible english :-/