I'll start with this gorgeous black and white photo:
First, I'll color the hair. I add a new layer above the photo, set it to multiply mode, and start painting away at her hair. I'll make her blond by using different shades of light yellow, gold, and brown. (I use the lightest yellow in the natural "highlight" areas of the photo.) In the diagram below, you can see the layer in normal mode and also in multiply mode. The layer is also set at an opacity of 80%.
Next, her skin. I made another layer, set it to multiply mode, and airbrushed different shades of peach and pink until I thought it kind of looked normal.
Because I was a little sloppy with the airbrush, I added a layer mask to clean up some of the edges:
Finally, I added yet another layer and painted on different shades of blue-again, the layer was set to multiply mode.
And here's my final result:
That took me about 10 minutes (the skin took the longest). If I were being paid for this project, I would probably duplicate the photo layer and play with changing the black/white using the hue/saturation dialog box to give the shadows more color. But then again, this is a free demo. So, enjoy!
More Tutorials: 
