A while back I watched a YT vid on how to DIY this sort of stuff with rattle-cans. Can't remember all the details (and can't now find the vid), but the process went something like..
- using fine grit paper, rub down all surfaces of the item
- spray the lettering in the highlight colour, applying 2+ coats (obviously, this results in lots overspray in and around the lettering)
- using fine grit paper, rub down all around the lettering and in-between the lettering as best you can - crucially, leave the top surface of the lettering un-keyed
- spray the whole of the item in the background colour
- using extra fine grit paper, gently abrade the background paint colour off the top surface of the lettering, thus revealing the highlight colour
I was pretty sceptical about how that would turn out, but the guy seemed to get a really good, convincing finish. The key (pun intended) was not providing a keyed surface for the background paint on the top surface of the lettering - this allowed it to be removed with gentle abrasion easily, thus revealing the highlight colour underneath.