Darker colours that go over a Lighter colour on the model - easy... Laser on Clear Film
If you NEED the white BG for Roundels (like RAAF) or SQN Badges (RAAF again), print on clear and cut a piece of white filme JUST smaller than the colour on clear.
Whites and Lights get challenging, as your run of the mill Laser can't do white, and most commercial (ie easy to use) screen printing stuff (Print Gocco, etc) doing give you good enough res... What CAN work tho is (wait for it) BRASS ETCHING! Have a go on 10thou or 20thou Brass!
You'll need to do a two sided etch - side one, will have the exact pattern you want, but in reverse; side two will have the 'positive' of the image, WITH some 'runners', frames, whatever you want to call them, to hold the middle of letters in place (like the middle of an 'O'). Etch them up, then AIRBRUSH into clear film, touching up with a brush where needed.
The advantage of the etch mask is a) totally reusable, so you can shoot mutiple attempts in one go and choose the best, and b) you can actually get into the brass with a sharp blade or micro file, to 'sharpen things up'... You'll want to go look up things like 'Press n Peel Blue' and 'Ammonium Persulfate' ((NH4)2 S2 O8 - comes as whilte crystals), which you'll find at Electronics Stores where they sell supplies for Printing your own PCB's.
PLUS, if you can make spray masks, you can also begin to make you own etch (you may want to looking into options like Ferric Chloride etchant, as it goes a bit slower; or Copper Chloride in Aqueous Hydrochloric Acid Solution (CCiAHAS), which I have never used, but have been told its pretty cool! -->
Stop using Ferric Chloride etchant! (A better etching solution.))