Yes, I color my own coloring book pages.
This is actually the template page I used for the Distant Star 01 lineart. I printed off the original pencil drawing at about 50%, then inked it with my Micron pens. The scanned-and-cleaned version of that is the lineart that I have posted up here at DA.
I used Spectracolor pencils (an old semi-pro/student brand; I'm not sure you can get them any longer. High wax content, a bit less pigment than the pro brands), and in the background I used Crayola crayons as well. The paper has a bit more texture than I'm used to using, so doing a solid fill like this took quite a bit of effort! But I like to know how different papers handle different mediums so that I can advise people if they have questions.
Colored version of my own lineart. USED. WITH. PERMISSION.
Color variation (original artwork on which the lineart is based):