I've used blank decal sheets for about 2-3 years. My first attempt was for a custom decal to depect a fictitious medical supply company using my cousin's last name and his two married daughters to apply on an old time railway freight car. I made up the decals, which were to be black, on the computer, printed them out on paper, and then put the decal paper in a Xerox machine at my wife's office. I Xeroxed the computer made logo onto the decal paper and it worked fine. I then needed some 1960s USAF lettering and numbering for a 1/144th B-52G. This time I used a HP Laserjet printer to print directly on to the blank decal sheet. The trick I soon learned was to spray the decal sheet immediately after printing with a coat of either gloss, semi gloss, or dull coat clear spray to affix the printing to the sheet. Again the finished decals were as good as any I've used from kits. I've not tried to print anything up in color, but understand individuals with an ALPS printer have had good luck.
Hope this helps.
Dick McC