title: Custom background/transparent background on UIBarButtonItem?
body: <p>How is this effect achieved? Code snippets are highly welcome.</p>
  
  <p>This can be seen in Notes app and other apps on the App Store.</p>
  
  <p>It seem that either the buttons on the navigation controller are transparent and show the custom background of the navigation controller or that they themselves have a custom background applied to them. Any ideas on how this is achieved?</p>
  
  <p>EDIT:</p>
  
  <p>Here is an example from the iBooks app for the iPhone. As you can see, not only the UIButtons, but also the segmented control have custom backgrounds. I'm thinking that there is a way to globally set transparency/background to different interface elements.</p>
  
  <p><img src="https://i.stack.imgur.com/Rlltf.png" alt="example">
  <a href="http://c0839932.cdn.cloudfiles.rackspacecloud.com/iBooks%201.1%20-%206.png" rel="nofollow noreferrer">http://c0839932.cdn.cloudfiles.rackspacecloud.com/iBooks%201.1%20-%206.png</a></p>