While I could learn and adapt to any scheme, I personally think that most colors draw more attention than white/off-white/light-grey. So it would make sense to show available seats in color (any color) and occupied ones in white/off-white/light-grey.
For one example, this is just what AA.com does. Go to aa.com, mouse over Reservations and click "view available seats", enter any valid flight number and date to see what their seat map looks like.