Katura and I are taking an Advanced Photoshop class today, taught by Frank Ippolito (http://www.productionpost.com/home.htm). One of techniques that he covered was using a layer mask to use your sketch as a texture in a finished, and now colored version, of your drawing. This image is my colored version of a sketch Frank provided for us to practice with. The day is grey and rainy, which matches the tone of my drawing.