Colt never made an 1851 Navy that they called the 'Civilian Model'. All 1851 Navies were .36 caliber. Silver (not nickel) plated BS/TG was an optional finish as was blued iron and polished brass. This just another one of Pietta's marketing strategies.
Fingers (Show Me MO smoke) McGee - AKA Man of Many Colts - Alter ego of Diabolical Ken; SASS Regulator 28564-L-TG; Rangemaster and stage writer extraordinaire; Frontiersman, Pistoleer, NRA Endowment Life, NMLRA, SAF, CCRKBA, STORM 327, SV115; Charter member, Central Ozarks Western Shooters
Cynic: A blackguard whose faulty vision see things as they are, not as they should be. Ambrose Bierce