title: change fillColor of selected CAShapeLayer
body: <p>I'm trying to change the fillColor of a CAShapeLayer when the
  layer it's contained in is touched.
  I'm able to change the background color of the tapped layer like this:</p>
  
  <pre><code>-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
  CALayer *layer = [(CALayer *)self.view.layer.presentationLayer hitTest:point];
  layer = layer.modelLayer;
  layer.backgroundColor = [UIColor blueColor].CGColor;
  }
  </code></pre>
  
  <p>This turns the background of "layer" blue as expected.
  My problem is how do I change the color of the CAShapelayer inside "layer"?
  Thanks!</p>