Jairus, I think I may have misunderstood you when you mentioned a line drawing to "contain" the colors. I DO use a reference photo...I import the photo into my PS doc and use it as a template to get the basic proportions (it's on a lower layer, and my illustration is done in separate layers on top of the reference photo. Once I get the basic shapes, then I take it from there with the various PS tools. The entire illustration is done totally in PS...but there's no initial line drawing. You know PS, so you know what I'm talking about.
When I did these the "old fashioned" way, I would project the image onto my illus. board with an artograph and do a quick pencil sketch on the board to lay down the basic shapes and areas of color...same idea, but different methed.