title: change navigation bar color of specific controller
body: <p>I have set a color of my Navigation bar in <code>Appdelegate</code> so my app uses same color for all the navigation appearing in different screens. But Now for one or two controllers I want to change the navigation color. I used this code in <code>viewDidLoad</code> of specific controller but It isn't working</p>
  
  <pre><code>self.navigationController?.navigationBar.backgroundColor = UIColor.whiteColor()
  </code></pre>
  
  <p>I have tried this code in <code>viewWillAppear</code> function too but still it doesn't work</p>