I read about this yesterday in a book called Design Essentials, Third Edition. It's by Luanne Seymour Cohen. As it is copyright, I can't exactly tell you how, but here's the general info:
Open a file in PhotoShop (CS), duplicate the layer (i'll say color for the name), make a adjustment layer (Hue/Saturation), use a smart blur on the color layer, (try 67.9 and 29 in the respective fields at high quality), duplicate the color layer (call it outline), then go to the Channel Mixer, and use monochrome at 24, 68, and 8 in the respective boxes, then go to stylize in the filter menu and find edges, then darken the outline layer, and you should be set. Otherwise, continue to make adjustments. With these steps, I made these images (the first one is original, the second is by these steps). Wow that was a long sentence. Good luck!
Chase