title: UIBarButtonItem is blue instead of image
body: <p>Here is what I have in my viewDidLoad method:</p>
  
  <pre><code>self.navigationController?.navigationBar.backIndicatorImage = UIImage(named: "back")
  self.navigationController?.navigationBar.backIndicatorTransitionMaskImage = UIImage(named: "back")
  self.navigationItem.backBarButtonItem = UIBarButtonItem(title: "", style: UIBarButtonItemStyle.Plain, target: nil, action: nil)
  </code></pre>
  
  <p>I am trying to have a custom icon image for my back button in my navigation controller. Instead of the image showing in it's original format, I am seeing the image in blue. <strong>How do I get the image to show properly?</strong>  </p>