Just as it happens when stamping, then coloring, many times the answer lies with two things:
- your cardstock, and
- your ink ... i.e. your printer.
Cardstock is still an important element when coloring, whether the image has been stamped or it has been laid onto the cardstock with a printer. I usually find that I need to use the same cardstock in my printer as I use for stamping-to-color.
Ink ... and your printer: Laser and ink jet printers use completely different inks and methods to produce images on paper. I'm not an expert on computer hardware, but I do know that between the two printers available to me, I can only color images from one of them. Alas, I cannot explain that in detail ... my "techiness" usually gets handed over to a more tech-savvy person for the big details in that arena.
In both cases, try your digis with what ever variety that you have available. You may well discover a better combination for your success with digis.