The real trick tool for doing decals is called an ALPS Printer. It has the ability to print white as well as colors. That's the good news. The bad news is they were expensive-about $500. And the consumer model isn't made anymore..... They are available on eBay, however. Last time I looked there were about a dozen for sale.

That leaves you with an ink-jet and white or clear paper. I have found that some brands of paper do not get along with my HP inkjet at all. One paper that I got from a train shop smeared badly. So you have to play with the paper and sealer.

Kelvin