I use decal paper, both clear and white, from Bare Metal Foil called Exerts-Choice. About the only thing I use these for is printing number boards for locomotives. I use the laser paper and work up a sheet and take it to my local Staples who gladly uses their laser copier to print me off a sheet for a small fee. Here's a link to the mfg's page. http://www.bare-metal.com/Experts-Choice-Decal-Film.html
bare-metal sells it for ink-jet or lazer, works well in home printers you seal the ink-jet after you print it, so the color done run.
Micro-mark has it as well - and laser. If you print a decal in 'body color', reverse image, it's a pretty decent way to get white lettering.
Print the area around the lettering the color of the body, and then the area that isn't printed is white.
Here's a good example of that. I played around with various shades of red until I found one that matched Floquil Signal Red, printed a red block reversed around white letters:
White decal paper is great for printing whole car sides of graffiti cars too, depending on your decal application skills. Sent from my ONEPLUS A3000 using Tapatalk