title: How to completely clear the background color of UINavigationController while transition in progress on iOS7?
body: <p>Everything has <code>clearColor</code> background in my app.</p>
  
  <p>I push those <code>transparent</code> <code>UIViewController</code>s to my transparent <code>UINavigationController</code>. It works but while transitioning, I see a <code>gray or some background color</code> until the transition is completed (until the push animation is completed). After that, background is correctly transparent. But both while pushing and popping that non-transparent background color (where I can't find a clue for that color) breaks the transition quality. It is visually very ugly.</p>
  
  <p>How can I prevent that hidden color that affects transition?</p>
  
  <p><strong>Update:</strong> OK. This flickering thing (the hidden color that appears between transitioning) only happens on iOS7+. This problem does not occur on iOS 6+.</p>