The greening in stock cIEM cables do not look like actual oxidization of the metals within... but a chemical reaction of the outer clear coating with the body's secretion. This is why I always get black stock cables.
Further, winegums, even if the wire is insulated with PE, which is the most common insulation found across all aftermarket cables, the metal within tend to oxidize regardless because the PE was done improperly. This is what happened with TWag v1, DHC's earlier wires, and some others as well. However, Whiplash corrected their problem with the v2, and DHC also managed to iron out the PE insulation with Neotech, and now it's amazing. DHC's PE is extremely clear looking, which is unique, and it is also glossy to the touch. Zero oxidation even with everyday use for an extended period of time. I'm not 100% sure but teflon insulated wires don't tend to oxidize, but this is just my short observation after owning only two teflon insulated cables. I've owned many more PE insulated cables however.