Shoutbox

Not at all. As I said, each window has its own different backgrounds... untill now I haven't found any shared background, and not even a way to replace ConvoWindows backgrounds.
And you still have the scenes, wich can give you headaches (but you can hide in some cases) and What's New in Contact List, that has another background...

So, "in suma", no, no universal background, each window has it's own set of backgrounds =)