title: Unable to set barTintColor with custom RGBa in iOS7
body: <p>I have a simple code in my viewDidLoad that changes the color of the navbar in iOS7:</p>
  
  <pre><code>if([UINavigationBar instancesRespondToSelector:@selector(barTintColor)]){
          self.navigationController.navigationBar.barTintColor=  [UIColor colorWithRed:33 green:50 blue:86 alpha:1];
      }
  </code></pre>
  
  <p>When the view loads, the bar is completely white. But if I change it to something like:</p>
  
  <pre><code>self.navigationController.navigationBar.barTintColor=  [UIColor redColor];
  </code></pre>
  
  <p>it works perfectly fine. Is it that some colors aren't supported, or am I doing something wrong?</p>