Material for Shift Knob

I've never made ANYTHING for myself in my shop, so I decided to make a shift knob for my new car. I'm looking for a dark gunmetal finish ( not a bright aluminum finish) that won't rust. I'm assuming I'm looking for a stainless steel, but is it the material, machining process or a second operation that gives the material the darker finish. Below is a link to what I'm looking for. I've never machined any SS in the shop.

ZERG Industries Round Gunmetal shift knob | ZERG

Thanks,
Marc