If you spoke to Customer Service, don't be surprised that you got an answer that wasn't 'complete', since most of those folks aren't 'gun' people and work away from the main plant.
They're limited to what they're told - nothing more - even their supervisors.
Colt likely doesn't -case-harden the hammers, because leaving the flats bright is easier and cheaper, and because sometimes small parts - when truly case-hardened - can warp, causing a dollar loss in replacement.
Vaya,
Scouts Out!