when a vehicle is ordered with dealer installed options, those parts are shipped from a company that services the gm dealers in the area. once vehicle is labeled as shipped ,those parts for that vehicle are then shipped from the warehouse to the destination dealer for that dealer to install. sometimes the vehicle does get there before the parts but most of the time the dealer sits on them vehicle arrives. as far as the old parts coming off if the customer wants them they can have them as dealer is not charged or paying for them in any way. most of the time customer doesn't want anything to do with them and I don't want parts in mislabeled boxes that I didn't buy from gm in my inventory.
as far as color matching and coming from the supplier already painted, any good bodyshop should be able to paint them and make sure paint doesn't come off unless something hard hits molding.