Have a look at the tweak "Black Navigation Bars iOS 5" in Cydia. I don't know if it'll work for the iPad, as it doesn't say, but maybe it's worth a try? Or, maybe it's a good starting point...
Tthat's the only tweak I know to make the navigation bar black. if that doesn't work - maybe a Google search of the Web may turn up something.
Good luck.
Marilyn
P.S. Oh, and I've deleted the other post you made on this topic. Posting more than one thread about an issue not only fragments the conversation - it's against our rules. Please keep to this thread for any further discussion on this issue. Thanks.