title: How to add gradient to ASDisplayNode or ASButtonNode
body: <p>I am looking to add a gradient background to an ASDisplayNode/ASButtonNode. 
  I have tried creating a gradient layer and adding it as a sublayer like this - </p>
  
  <pre><code>CAGradientLayer *gradient = [CAGradientLayer layer];
  gradient.frame = button.frame;
  gradient.colors = @[[UIColor redColor], [UIColor blueColor]];
  [button.view.layer insertSublayer:gradient atIndex:0];
  </code></pre>
  
  <p>where <code>button</code> is of type <code>ASButtonNode</code>, but this just gives a white background to the button. I haven't been able to find much documentation for achieving this either.</p>
  
  <p>How can I go about adding a background given an array of <code>UIColor</code> and a <code>CGFloat</code> angle?  </p>
  
  <p>Thanks</p>