SelectedItem color (ContextActions)

I added to my View Cell the context Actions as described here https://developer.xamarin.com/guides/cross-platform/xamarin-forms/user-interface/listview/interactivity/#Context_Actions
The context action bar (and the actions) work well, but I don't know how to change/set the color of the selected item (now it's transparent, so user don't know how item is selected)