I used a caliper paint kit from Savage off ebay. It was applied with a brush.
It's really thick paint and self-levelled well, leaving a nice gloss finish. It took 48 hours until it was touch dry and you don't want to handle the calipers for a few more days after that as the paint is still soft. It eventually dries to a very hard finish. You don't want to go over a bit you've already painted until it's totally dry - just put on a decent coat and then leave it alone for a week. Make sure the calipers are as clean as possible before painting.
The bike has done zero miles so I can't say how it will last. But I can confirm it's definitely very resistant to brake fluid after some careless bleeding.
