

What is this blue oxide/rust effect and how to paint it?
I am about to start painting my Iron hands and I’ve decided to go with the vanilla 8th edition supplement color scheme. The only thing I can’t really get is what those little blue oxide effects on white weapon casings are. It adds a cool detail but I can’t figure out how to achieve that while painting. Is it possible to do it with the Vallejo Blue Color Set I have?
upd: sorry for the pic quality, hope you get the idea