I sprayed a stem and a few other bits and pieces with Hammerite Direct To Rust spray paint (satin finish) and they came out very well indeed, it gives a durable finish (just leave enough time for the paint to harden, a few days at least, a week even better)
A good key, etch primer, and decent quality satin black car paint looks brilliant and is plenty durable. Done many a lever, clamp, derailleur cage etc like this.
Ref: seatpost - I intend to find the 'right' position then mask off the hidden bit and spray the exposed part.
Ref: satin finish - not quite what I'm looking for. It looks nice, but the bits on my Technium look pretty gloss to me. I think the epoxy stuff might do the trick.
Another vote for satin black. Use etch primer on alu parts for best results. Another tip is to use your oven to bake the paint, saves time waiting for it to air dry - hang parts from the racks using garden twine or similar stuff. 50 degrees is enough between coats then give it 20 mins at 100 degrees when finished.