I've noticed that a lot of the cheaper Hunter Arms Fulton and Fulton Special guns with their cyanide colors retain more vibrant colors than their better quality L.C. Smith cousins which had bone charcoal case colors. I am, of course, taking overall condition of the guns into consideration here. I also think Daryl is right about the Folsom Bakers vs. the earlier Baker guns. I still have my first shotgun, a Stevens model 220 single shot 20 gauge which has cyanide case colors that are quite strong and vibrant despite the gun having seen a lot of use.
But I agree with Miller that bone charcoal colors are much more attractive, even when somewhat worn. I don't think it takes a great deal of care to maintain case colors though, and I feel that somewhat acidic or salty perspiration from your hands probably does more damage than sunlight ever could. Because of this, a wax or clear lacquer coating is probably helpful as long as the wax used does not contain abrasives. A Thompson/Center Hawkin flintlock I own is over 40 years old, and despite a lot of usage and carry, the colors are very strong with no more care than the usual hot water cleaning and oiling after the gun is dried. This includes the areas around the pan and frizzen that get coated with corrosive black powder fouling.
