My point of view in the discussion is that the colors are oxides, and not likely zinc oxides. Iron oxides are not likely to be chemical compounds, but rather chemical reactions. The "discussion" seems to be, can sunlight provide the energy to drive the chemical reaction, to create new oxides on case colored gun surfaces, which results in a different visual appearance.
Earlier, there did not seem to be dispute that hidden, internal gun surfaces, may very well be protected by various traditional and modern oils, probably for corrosion and wear resistance. But, that is a general area of many guns, where case colors do not seem to be affected, or as affected by the appearance of fading.
