title: How to change SCNPlane color as clear color
body: <p>I am working on a ARKit project which needs Ripple animation effect when tapped on Horizontal Plane. For that I have took UIView object and pass that as contents for material of SCNPlane object. I have added Ripple animation to UIView object. Everything works fine. But I can't change the SCNPlane colour to clear color. I can use transparency property for the material. But it is hiding Ripple animation too. So, what I need here is, the background colour of SCNPlane object should be transparent and only Ripple animation should appear to user. Can someone help me on this.</p>
  
  <p>This is my code.</p>
  
  <pre><code>    let location = tapGesture.location(in: self.sceneView)
      let results = self.sceneView.hitTest(location, types: .existingPlane)
      if !results.isEmpty{
  
          guard let result = results.first else{ return }
          let myUIView = UIView(frame: CGRect(origin: .zero, size: CGSize(width: 300, height: 300)))
          myUIView.backgroundColor = .red
          let plane = SCNPlane(width: 1.0, height: 1.0)
          plane.firstMaterial?.diffuse.contents = myUIView
          let planeViewNode = SCNNode(geometry: plane)
          planeViewNode.eulerAngles.x = Float(-Double.pi / 2)
          planeViewNode.position = SCNVector3(result.worldTransform.columns.3.x, result.worldTransform.columns.3.y, result.worldTransform.columns.3.z)
  
          self.sceneView.scene.rootNode.addChildNode(planeViewNode)
  
          //Ripple animation code goes here 
      }
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/WCetq.jpg" rel="noreferrer">I took screenshot from Civilisations AR app from BBC. Please refer the screenshot by clicking this link. This is how exactly I need.</a></p>