Like everyone else has said, those colors are cyanide. There are quite a few Spanish guns that use this method as well as the Turks.

If you look at the bottom gun, 3rd post, page 1 of this link, you'll see a Turk made Hatfield with the same type of colors:

http://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=24270&page=1

Best!

Greg


Gregory J. Westberg
MSG, USA
Ret