I wouldn't worry too much about minor discoloration of the wire but I would closely inspect all fittings and the wire-to-fitting joints which are the weak links in any
rigging. The terminals, swages and
turnbuckles will likely go before the wire and a thorough
rigging inspection sounds in order here. I'd also quickly check the rigging with a magnet to make sure someone didn't replace the original Hunter 316 stainless wire with a cheap substitution which has ferrous metal in it to cause the rust. You can polish the wire but the reason it shows rust concerns me and just cleaning it won't fix the problem.