title: SceneKit: animation of SCNView background color happens instantly, not gradually
body: <p>Animating the <code>backgroundColor</code> property of a <code>SCNView</code> happens instantly, instead of gradually over the specified duration.</p>
  
  <p>Here's the code:</p>
  
  <pre><code>UIView.animate(withDuration: 0.5, animations: {
       self.sceneView.backgroundColor = UIColor.redColor
  })
  </code></pre>
  
  <p><a href="https://stackoverflow.com/questions/3762561/how-to-animate-the-background-color-of-a-uilabel">This question</a> is similar, but its solutions didn't work. Specifically, setting the <code>backgroundColor</code> beforehand and animating against the <code>layer</code> property did not help.</p>
  
  <p>How can you animate the <code>backgroundColor</code> of a <code>SCNView</code>?</p>