title: How to animate the opacity of a SKShapeNode?
body: <p>I am working on the instructions screen of my game and want to show to the user that they should tap a certain area of the screen. </p>
  
  <p>So I want to show an animation where </p>
  
  <p><strong>1)</strong> A finger is scaling in and out of the screen, followed by -- <strong>working fine--</strong></p>
  
  <p><strong>2)</strong> A rectangle changing opacity (to show to tap there) and then -- <strong>need help--</strong></p>
  
  <p><strong>3)</strong> A text flashing saying, "Tap here" -- <strong>need help--</strong></p>
  
  <p>For <strong>1)</strong>, I have this (working fine): </p>
  
  <pre><code>    finger = SKSpriteNode(texture: fingerTxt)
      finger.position = CGPoint(x: 330, y: 450)
      finger.zPosition = 10
      InstHolderNode.addChild(finger)
  
      let fingerTapScaleDown = SKAction.scale(by: 0.6, duration: 0.7)
      let fingerTapScaleUp = SKAction.scale(by: 1.6, duration: 0.7)
      let fingerScalingSequence = SKAction.sequence([fingerTapScaleDown,fingerTapScaleUp])
  
      let fingerTapScaleForever = SKAction.repeatForever(fingerScalingSequence)
      finger.run(fingerTapScaleForever)
  </code></pre>
  
  <p>For <strong>2)</strong>, I have : </p>
  
  <pre><code>    var rect = SKShapeNode(rectOf: CGSize(width: 150.0, height: frame.height * 2))
      rect.position = CGPoint(x: 300, y: 100)
      rect.fillColor = SKColor.brown
      rect.alpha = 0.5
      InstHolderNode.addChild(rect)
  </code></pre>
  
  <p><strong>Question :</strong></p>
  
  <p>How do I sync <strong>1)</strong> and <strong>2)</strong> such that after <strong>1)</strong> is completed (the finger tapping animation is done), <code>rect.alpha</code> value to change to <code>0.1</code> and then changed back to <code>0.5</code> and then  <strong>1)</strong> happens and then <code>rect.alpha</code> is changed to change to <code>0.1</code> (in a loop) continuously.</p>
  
  <p>Many thanks!!</p>