initDisplay

AppDelegate.m

CGRect viewRect = [[UIScreen mainScreen] bounds];
self.window = [[UIWindow alloc] initWithFrame:viewRect];
UIViewController *viewController = [[UIViewController alloc] init];
UIView *colorView = [[UIView alloc] initWithFrame:viewRect];

colorView.backgroundColor = [UIColor darkGrayColor];

viewController.view = colorView;

self.window.rootViewController = viewController;
[self.window makeKeyAndVisible];