To my knowledge, Nikon used a type of copper-aluminum-silicon alloy for the chassis of the FE/FM series of cameras, and probably for many of their cameras after. I'm not sure about the material used for the top and bottom plates. Denting has a lot to do with the thickness of the material used. Whether the revealed color is yellow or silvery may have to do with the specific alloy composition, or even the environment the material is exposed to.
What we call "brassing" is not always revealing brass - Brass is rather heavy (dense) and not particularly stiff for its weight. It's very ductile and resistant to galling which makes it easier to machine and a good material for threaded moving parts like lens helicals, filter rings, etc.