It’s pretty much agreed that it’s impossible to create light colored (yellow) decals to go over a dark (black) background with an ink jet printer without using white decal paper. How about with a color laser printer? Does anyone have any experience with that?
Color laser printers work on the same principle as inkjet printers do. They need the white paper to let the color show up. A simple test would be run some colored paper, the same as your engine/car, thru the printer and print the art work to see what it will look like. A trick some guys use, especcially with black, is to set up the artwork in the color you want to print and do a black background (or a matching color to the project) to cover all of the white around the artwork. Print this on white paper and you should have the artwork show up fine with a dark background.
When you apply this to the model, find some body seams such as door seams on an engine to have the edges of the decal fall into. When you do this you can then hide the thin white edge of the decal with some matching color. The good thing about laser printed decals is you do not have to seal them before installing them as the toner is fused to the paper and is not a water soluable ink like inkjets are. There are also some waterproof inkjets out there
This HO-scale loading dock door illustrates one of the problems of getting light-on-dark letters.
I painted a white rectangle on the door, and applied a white-on-black image with clear decal paper. Unfortunately, the color saturation of the black background just isn’t very good. After I applied the decal, I painted over the door with acrylic craft paint. Since this building is in a dark corner at the back of the layout, I wasn’t too fussy about getting a good paint job around the lettering, so the image remains as an illustration of the problem.
I suspect that you would get better color saturation for a black background using a laser printer. This was done on an inkjet.