ypically, you use natural ABS with a colorant, or masterbatch, as it is called in the industry. Here's a picture of master batch pellets, and a few test prints using Filastruder filament
So, you'd mix those pellets with the natural ABS pellets, usually at a 50:1 ratio, or whatever is specified by the manufacturer of the masterbatch. Then you get this:
You can get colorants (and ABS pellets for that matter), from our partner, OS Printing LLC. Check them out at store.osprintingllc.com.