I use one of those "inkless ink pads" that doesn't leave black residue on your hands. The prints come out much lighter than I thought they would, and I haven't had any problems across many fingerprint cards (mine, and others I "roll" them for).
I had rolled mine with an old fingerprint setup I kept in my office for work stuff but they were light so I ordered a fresh ink pad for a few bucks off amazon. While I was waiting for it I saw that a different model ink pad from the same company was selling a pad that was clearly marked BLACK (the other wasn't), so I ordered that one too and held off on sending the cards in. Long story short, both new pads resulted in prints that were nearly identical, darkness-wise, to the set I rolled on my old office ink pad. I sent them in and am still waiting to hear back, but it's good to hear that the inkless ones are cool.