Small parts on many fine guns were not case colored, rather were nitre blued or so called "fire" blued, same thing. I would think really small parts likely would not take a mixture or blending of colors, and would come out in a single color anyway. Also that level of heat might not be kind to parts as small as you suggest. Nitre bluing has the capability of producing a fine straw almost gold color at lower temperature levels, similar to the triggers and side plates on pristine condition original Lugar pistols. I use that to color my triggers on doubles I refinish. Suggest your friend consider nitre bluing.
