title: Changing color of an MKOverlay that has already been added to a mapview
body: <p>I have some MKOverlays(actually they are MKPolygons) that are loaded as soon as the map shows up.  I would like to change their color dynamically.  The only way I can see of doing this, is to remove the overlay then add it back with the new color.  Is there a better way to do this on the existing overlay?</p>
  
  <p>I am brand new at objective-c/xcode/ios ... so please be gentle :)</p>