Multiple MKPolygon changes color after zoom level changes

Question

Hello i am working on map related app in which i have to draw multiple polygon on mk mapview. it's load fine at first time .

As you can see in image.but if i change the zoom level all the colours are changed in mapview as shown in picture below.

-(MKOverlayRenderer *)mapView:(MKMapView *)mapView rendererForOverlay:(id<MKOverlay>)overlay
{
 if([overlay isKindOfClass:[MKPolygon class]]){
MKPolygonRenderer *renderer = [[MKPolygonRenderer alloc] initWithPolygon:overlay];
            renderer.fillColor=noflyzonecolor;
            renderer.strokeColor=noflyzonestrokecolor;
            renderer.lineWidth=strokeWidth;
  return renderer;
}
}