All brand new ones from the dealer come with just an undercoat. It's up to the seller to either pay the dealer to paint it or get it done privately. Cost me £60 to get it sprayed and fitted from a friend.
Shouldn't be a problem wrapping a primed spoiler. I would guess they are bonded on but there may be bolts and so some drilling required. generally though if there isnt existing holes then bonded would be the way to go