Wasn't Concorde extremely fuel-efficient at M2 and 60,000', but the horrendous fuel consumption getting up there more than offset that?
Smokey engines were a feature of the pre-production machines. The production Concordes with a change in combustion chamber design had a much cleaner exhaust.
Turin has it on why Concorde didn't sell - massive increases in oil prices and perhaps more importantly, the advent of the wide body airliner in 1969 that changed the airlines' focus from speed to per-seat operating cost reduction, where it remains today.