A: Generally, inks used for no-line coloring are pale and tend to "disappear" when colored over. Any pale ink can work, though you'll need to choose an ink that is compatible with your coloring medium. I have used pale yellows, pinks, and greens as well as neutrals (beige or grey). As for specific brands, I usually reach for either the Impression Obsession Mist Hybrid ink or Ink On 3's Fadeout ink (also a hybrid) - they are about the same pale neutral grey, and will not bleed when used with watercolor or alcohol ink. The Fadeout lines soften and blur after some time, adding to the no-line effect - that is a unique feature to that ink. Check out these no-line coloring techniques:
No-Line Coloring
No-Line Watercolor