This article — which is so full of win that the rest of us will be on win-rationing for the next three days — explores this issue in detail:
One possibility is to alternate the colors, creating a vast checkerboard effect that in long camera shots would create the illusion of occupancy. Another plan — painstaking, but bold — would be to paint on each seatback the likeness of a chubby youngster.
I’d probably go with a lighter, seafoamy green. At least if they couldn’t make the chubby youngster option work.