It looked like orange rust. I used Blue Wonder rust remover on it, it got most of it, but left dark streaks. What bothers me is that I have several handguns, both blue and stainless-this is the first I have ever had rust on me. I have only owned this XD for just over a month, most of my guns are several years old. Is this slide stainless steel? Seems I once heard that stainless would rust faster in places where it comes in contact with carbon steel, perhaps the cutters used for cocking grooves and sight dovetails are responsible for this? As for lube, i've been using Tetra oil and grease for the last year or so.
My Bi-tone slide has discolored!?
I went to a considerable amount of trouble and extra time as well as higher cost in obtaining a Bi-tone sub. Imagine my chagrin upon discovering that it has started to rust! I have kept it oiled as much as any of my other fireams and was not expecting this at all. If this finish is hard chrome, it has to be the thinnest application I have seen to discolor this way! It has spots in the cocking grooves as well as along side the front and rear sights. 
