I've been digging through the apple documentation, but I can't seem to find how some apps change the colour of the status bar (with your signal strength, etc in it) to black? I'm guessing it's just a one line call somewhere?
You may also want to set UIStatusBarStyle = UIStatusBarStyleOpaqueBlack in your Info.plist, so that the Default.png shows a black status bar instead of the gray one before your application is loaded.
This is a very similar question to the OP, but is there any way to change the navbar-style to black through the info.plist as well? Right now I am doing it through code, and while this works it creates a bit of a delay, where first the navbar is black and then after about a second, once the program loads properly turns black.