Here's a little somethin' I did awhile back for a workbook cover that covers the stages from concept to finished product via digital coloring.
The Sketch
Not much to it; just the standard begining and in this case, no computer, just a #2 pencil and a sketch pad.
Computer Inking
I scanned my sketch into the computer, but only at 72dpi because I only needed a low res image to trace in Adobe Illustrator. This outline became vector art, so I was able to manipulate the size there after with no worries. I then imported this outline into Photoshop where it became bitmapped, yes; but the outline is VERY crisp and neat. You can also see changes happen that were made during meetings with the editor.
Base Color
Now using the magic of layers in PS, I colored the robot with simple base colors. The outline remains on the top and the various color layers fall beneath it.
Final Rendering
Once again using more layers and adjusting their properties on how they react with layers below them; the shading and highlights are added. Now I just hand the final artwork over to the designer who uses it as needed, in this case it was placed on the cover of a work book for students.