title: Transparent NSCollectionView Background
body: <p>I'm again struggling with setting NSViews background colors to transparent. I have a <code>NSCollectionView</code> as part of <code>NSClipView</code> which is part of a  <code>NSScrollview</code>. My <code>MainViewController</code> has an outlet to the <code>collectionView</code>. With adding the two lines of code and after compiling the background is sometimes transparent but most of the times not:</p>
  
  <pre><code>view.wantsLayer = true
  collectionView.layer?.backgroundColor = NSColor.clear.cgColor
  </code></pre>
  
  <p>I also tried to select/de-select the "Draw Background" property of the <code>NSScrollView</code> in the IB without any effects.
  What do I miss here. </p>