This must have been asked before, but after Googling I still can't find the answer.
How do you change the color of the title bar (The bar that you can click and drag around with the close, minimize and maximize buttons) to a different color than the default gray in Cocoa?
If you set the background color of a "textured" window (a distinction that isn't really all that visible in Snow Leopard) that color will be applied to the titlebar as well. This is what Firefox does.
I would recommend though not having a real titlebar (i.e. setting your window to have no titlebar) and using +[NSWindow standardWindowButton:forStyleMask:] and putting your own buttons in the "titlebar". This allows you more control and is way way less hacky.