title: Sprite Kit: change backgroundcolor with ColorizeWithColor
body: <p>Is there a way to change a scene's background color gradually, instead of it swithcing colors at once?</p>
  
  <p>In my scene, I have a button that sets the background color to a different color than the color that is called in the initial creation of the scene, simply like so:</p>
  
  <pre><code>-(void) newBackgroundColor
  {
      self.backgroundColor = [SKColor blackColor];
  }
  </code></pre>
  
  <p>However, (of course) this switches the color from my initial color to black instantly whereas I would like it to change much the same like nodes do using <code>colorizeWithColor:</code> where two colors 'fade' from one to another. My guess is I would need to implement an <code>SKAction</code> before setting the new color, but the <code>backgroundColor</code> property does not seem to support the colorize action.</p>
  
  <p>Is this possible? I have not been able to find out how so far.
  Thanks</p>