I think what you would have to do is print your Have Glass markings in two passes. Do a pass that prints just white (or black in your photo editor) to give it a good, white foundation. Then do your final, grey color over the top of that, maybe making the markings a pixel or two bigger so they just barely overlap the white so you don't have plain white peeking out along the edges.
I have an HP Color Laserjet that takes the ghost white cartridges, but haven't bought a Ghost White cartridge yet as I haven't had a need to up to this point. I can tell you from experience, however, that the operating costs of a color laser printer such as the one from HP that I have are actually lower than the costs associated with inkjet printers. Since inkjet cartridges are no longer the sealed systems they used to be, you can easily spend 5 to 10 dollars a page if you print infrequently, because they dry out as they sit. No such issues with laser printer toner.
With the right decal paper (I use Sunnyscopa White Laser Decal Paper) a laser printer also eliminates the need for applying a clearcoat to your decals to waterproof the ink. With that paper, I can go from printer, to water, to model in minutes. You can also use all of your normal setting agents and solvents on those decals, as there is no clearcoat on them to become a gooey mess. There are a few that are still stuck in the "you must clearcoat, even with laser printers" rut, but it simply isn't true anymore.
In short, a laser printer (even a cheapie like an HP) is a good investment in general, and even more so if you want to make your own decals and use Ghost White Toner.