Tolly
If the Colt in question is really old (19th century), chances are it is nickel plated. Some custom order guns might also be silver plated, but typically that was used on engraved presentation pieces. Nickel plate was applied on top of a thin layer of copper plate, as the nickel would not bond directly with the metal surface of the gun. If your Colt is a more modern revolver then it may have been bright chrome plated after it left the factory, or it may be an electroless nickel finish, as this was used by Colt for a number of years before they went to stainless steel.
Generally speaking, at least to my untrained eye, nickel plate is not as shiny as chrome plate, having somewhat of a slight golden cast to it. Chrome plate appears to be shinier, with a silvery, almost mirror-like finish to it. Hope this helps.