Ah I see what you mean. I’m not a fan of different coloured tattoos, meaning yellows etc specifically. Dark blue might work, it would probably mix in better anyway.
I noticed this design has some shading on the outside of the lines, I’m not sure if this would work/help, but I quite like how it looks:
Edit: Image didn’t seem to work, here’s the link:
http://img68.imageshack.us/my.php?image=backtatut7.jpg