If it has a yellowish hue to it, it's likely to be nickel plated. That would be called a MK II, but MK II was never engraved on 'em that I know of. It was when plating became available that they had to distinguish between the blue and the nickel, so the blue was called MK I, nickel MK II, and chrome MK III. Later a shiny blue was called a MK IV. Hundreds of MK II's were made, so it's likely not worth a whole lot more just for its nickel plating. The blue guns go for about 450 to 500, depending on condition and how bad someone wants it. Stainless guns go for about 550 to 600. If yours is in good condition, it could likely be worth 500 or so.