I can sympathize, with your difficulties, Don.
Having printed out a fair number of my own decals, I've never been able to closely match a dark colored surround to a background paint job. Even when the hue was perfect, the saturation has never quite looked right. The only "fix" I've been able to come up with is touch-up painting around the image before cutting out the decal--not a big issue for nose art, but pretty tough around any kind of lettering.
I had that same "ink runs no matter what" problem when I switched from a dead Lexmark printer (which had always worked flawlessly for decal-printing) to a 2nd-hand (free) HP printer--no matter what combination of decal papers and/or sealants I used (and I tried them all), the colors always bled. Sometimes it was as much as two weeks after the clear-coat, which was truly frustrating. I eventually got a new low-end HP printer that came free with my new computer, and did a "what the h***" test run, expecting the worst, but all was fine. Evidently the different print cartridges it used had some different formulation of ink as well. Based on my experience, it seems an ink-problem, rather than a sealant problem.
Not much in the way of help, I know, but I feel for you.
Regards