The cars are on an assembly line. They are dipped through a sealer, then primed and painted with automated robots. The interior/engine bay paint is the same basecoat as the exterior color just without flake/pearl/ and clearcoat. So that means the color that you see inside your car is the BASE paint without the extra additives. Once the whole car has been sprayed, it goes through a series of finishing touches such as the finishing base and the clearcoat.
It wouldnt be very smart as an automaker to paint a car twice, or with two different colors. Also, the color of the paint has no effect on it's cost. Maybe if you have black base with gold and platnium flake, then its going to cost more.
I dont mind discussing what color my car used to be, I'm simply saying that it's not purple.