title: Global changes UINavigationBar background using appearance proxy not working
body: <p>I'm trying to change some properties of all UINavigationBars in my app using UINavigationBarAppearance.  I'm calling the following function in <code>application(_:didFinishLaunchingWithOptions:)</code> in AppDelegate.swift:</p>
  
  <pre><code>func customizeAppearance() {
  
      let navBarAppearance = UINavigationBarAppearance()
      navBarAppearance.configureWithDefaultBackground()
      navBarAppearance.titleTextAttributes = [NSAttributedString.Key.foregroundColor: UIColor.white]
      navBarAppearance.backgroundColor = UIColor.black
  
      UITabBar.appearance().backgroundColor = UIColor.black
  
      let tintColor = UIColor(red: 255/255.0, green: 238/255.0, blue: 136/255.0, alpha: 1.0)
      UITabBar.appearance().tintColor = tintColor
  
  }
  </code></pre>
  
  <p>I expect this to change the background color and color of the title text, but when I run the app, only the text color changes (this is also true for the UITabBar).  Any suggestions?</p>