The original line art was done by Tom Hodges of DeviantArt. All I did was vector the lines to give it a solid look and initially apply flat colors. Only after the flat colors were done, I changed the colors to B&W to emulate the look and feel of an actual inked line art. This work is one of the very few that I actually did a shading/highlight.
Here’s a quick comparison of the original line art by Tom Hodges and the colors that I did in Photoshop: