Geno, per a discussion with Dr. Gaddy, the case color film is very thin and loosely bound. It provides very little corrosion protection; the bulk of corrosion protection comes from the high carbon content of the case "skin." The use of a clear coat (wax/drying oil/lacquor/poly/etc.)is for abrasion protection for the color layer. As above, there are many ways to make a grey finish on steel.