S-John,
I have asked the same type of question around the internet for over 5 years because of similar issues (greying/discoloration on a Citori) without getting a satisfactory answer. The discoloration seems to come from acidic hand sweat. I use Flitz to polish it up and it works well.
It seems that the lack of good info stems from "Silver Nitride" being a marketing name of a hardening/coloring process that most probably does include any Silver Nitride (highly reactive and unstable).
I've heard that Silver Nitriding is:
*Plasma nitriding
*Plasma enhanced chemical vapor deposition
*Electoless nickel
The plasma coatings are PFM to me, so I quit looking around.
Edit: Gil, PFM is a high technology acronym; Pure ----ing Magic.
