This was actually really fun to do! I recently started doing this (as in yesterday). It works better than using a regular pencil because reg. pencils are grey which is really hard to seperate. I used these weird red twisty pencil things I found in my mom's art stuff (I took with permish!) but I bet this works with any kind of colored pencils. The cheapest oughta do, actually (since it's only used as a guide for your ink, anyway.

I think this works in GIMP and PaintDOT too, but I don't know what the settings are!! QAQ
I might switch over to Pear OS (Linux knock-off of Apple OS interface) since this computer is lagging, and that would work better... but I'd have to give up the complexities of Photoshop i'm still learning and came to love emmensly... nnnnn.... if I do switch over, I'll GIMPify this tutorial since apparently a lot of people use GIMP.

... I myself like the feather icon of the old Photoshop, though. (Does GIMP have a smear tool and opacity layer setting? I'd die without those.)