title: How to make blinking button from two images objective c sprite node
body: <p>I want to create blinking button from two images using sprite Kit, now I have :</p>
  
  <pre><code>resButt = [SKSpriteNode spriteNodeWithImageNamed : @"retry.png"]
  </code></pre>
  
  <p>I saw couple posts about how to do it using UIButton, but my question is how to do it in Sprite Kit using objective c? </p>