New airliner painting question

Today I saw a new 737 heading to Spokane International Airport in a factory fresh “green” unpainted condition.
There is a firm there, “Associated Painters” with a new purpose built facility there that paints aircraft. I know high end bizjet and new Viking Twin Otters receive paint there and I’ve seen photos of Southwest Airlines 737s at the facility too.

My question: who would have been flying the new jet for paint? A Boeing crew, customer crew, or freelance?

Spokane/GEG is just a 45 minute flight from Renton, so it’s easy to get the jets here from Boeing.

-Would an airline contract with the firm or is the first paint part of the purchase price and be contracted by Boeing?

-And are they complete when painted or would they have to return to Boeing or another contractor for final interior work?