I personally liked the idea of rust as camouflage. Not terribly realistic in space I know, but still.
Perhaps something else to make the ship look more worn though. Some rough patches to make it look like the hull was degraded by radiation, some pock marks from micro meteorite that hit when the shields were down (or perhaps a different looking spot form where nanobots repaired this damage) and maybe a scorch mark or two either from weapons fire or, more likely, from getting too close to a mine.