When you open MainWindow.xib in Interface Builder, you can find "Window - Status Bar" and "MainViewController - Status Bar". Setting either one or both as "Black" doesn't seem to have any effect on the actual application. Your statusbar remains gray.
So how do I get a black statusbar?
Open your application .plist file, click on plus icon (+) to create a new row and write "Status bar style" as name and select "Opaque black style" as value.
Those are "key = UIStatusBarStyle" and "string = UIStatusBarStyleOpaqueBlack if you're more familiar with that style.