They're not going to have a livery...the airplanes will be nondescript. Upon signing the flight release, the captain will be handed a little lighted sign on suction cups much like Little Caesar's Pizza delivery, which he will attach to the roof just before boarding. It will say, "Amazon Airlines - operated by XXX" or some-such, only the "XXX" part will be in magnetic letters for easy later revision. The captain will be responsible for turning the sign back in at the end of the trip.

I got that from a usually-reliable source.