All Class 800/0s are vinyl. Everything else (including the 800/3s) is painted.
It is more obvious to see from above where the roofs of the 800/0XXs are white. Take at North Pole depot on Google Maps.
Apart from the number, I don't think there are any external differences between the 800/3s and the 802/1s.
I think it's easier to spot the paint/vinyl difference at the intra-unit carriage ends - green if painted, silver (I'd say, rather than white) underpaint if vinyled, as that doesn't cover the ends either.
The other giveaway of original
IEP▸ order vs AT300/802 (pointed out on that earlier thread) is the resistor box on the roof - roughly square for the former, much longer than wide for the latter. It is possible (depending on whom you believe) that the braking resistor is the only significant difference between the two order types now.