I don't think that you can change the tintcolor. Since iOS 6 such viewControllers are based on remote view controllers, meaning their view is completely owned by another process and inaccessible programatically.
This can be confirmed by looking at the recursive description of the controller's view:
<UIView: 0x140b0780; frame = (0 0; 320 568); layer = <CALayer: 0x140b0860>>
| | <_UISizeTrackingView: 0xe3b7300; frame = (0 20; 320 548); clipsToBounds = YES; autoresize = W+H; layer = <CALayer: 0xe3b7410>>
| | | <_UIRemoteView: 0xe3b9b80; frame = (0 0; 320 568);
The _UIRemoteView
indicates that the contents of the view is hosted in another process.
Edit:
Curiosly with MFMailComposeViewController
it works. This viewController has an addressable navigationbarcontroller.