title: UISwitch thumbTintColor removes shadow
body: <p>I'm creating an app that has a UISwitch. I changed the thumb color to match the background (using <code>thumbTintColor</code>) and the shadow on the thumb is removed. The result is the thumb vanishing when it is in the off position. </p>
  
  <p>Does anyone know how to add a shadow to the thumb, or prevent it from going away?</p>