Color of the smoke doesn't matter, and as the engine heats and burns more of the mixture, and more efficiently, there will be less of it.
As for smoke off the engine, that's no doubt residual crap splattered on there from workin on it previously...it'll smoke, stink, and make you panic a bit, but it's no threat to the operation of the vehicle, no.
Fire it up and let alla that crap burn off, and then take her out and do a safety-check (brakes, lights, etc) and if it passes that....punch the throttle to the stop and ride full-out for a while to help alla the crud burn off.
And after having ridden it for an hour...come back and tell me if you still wanna sell it...I suspect there might be a little reluctance, after that...heh heh heh.
-Ree