....#4. The "stuff" is not blue/red/straw in and of itself. Rather, various thicknesses of coating cause reflectance of various wave lengths and we see them as differing colors. Blued/blacked metal appears dark because the oxide coating absorbs most light and reflects little. Note, the prismatic colors we see from a puddle of water with a bit of oil on top is caused by varying thickness of the oil film....
This is a tough one. It's been noted by Doc Gaddy and others that the colors reflected off an oil film change as the viewing angle changes, but color perception of case colors doesn't.
The oil film is more or less tapered and as you change viewing angle, the film you are looking through will be more or less thick and will reflect light at changed wave lengths. The CC films are more uniform in thickness and the viewing angle has little effect on them.
It might also be supposed that fading of case colors may not come from wear, if wear can be assumed to be a decrease, change, in thickness of the reflective layer.
The CC films do not wear down in decreasing thickness. Rather, it loses particles a few at a time; remember that the particles are loosely bound and can be knocked off. Each time a few particles are knocked off the CC fades a little. When most of the particles are removed the light reflected will be from bare steel until the steel gets a surface of oxide.
DDA
