I want Air shown above Native

i did coding on xcode :

UIView *airView;

        UIViewController *vcl;

            vcl = [[[UIApplication sharedApplication] keyWindow] rootViewController];

            airView = vcl.view;

        airView.backgroundColor = [UIColor clearColor];

[self.freRootView addSubview:self.readerView];

        [self.freRootView sendSubviewToBack:self.readerView];

but, got a gray background.