Below is a gallery of hand painted color guides from the colorist at DC, Bob LeRose.  Several of these complete mini-comics have hit eBay over the past few years (notably Batman, Joker, and Penguin).  The color guides are hand colored and coded with color codes recognizable by the printers that produce the final product.  These are usually photocopies of the original artwork, then colored on by the colorist.

Buyer beware:  There have been several fake copies of different pages that periodically hit eBay.  The description is very misleading, says it’s an “original art reproduction” or something similar, to lead you to believe it’s original but stating somewhere in the listing that it’s a copy.

This is the same process used in regular comic books.  See also:  Mini-Series Hand Painted Color Guides