In the current furry render challenge blurb, it states that entries with Postwork and or cel Shading are welcome

Where would you start with cel shading, I presume that the author is referring to the tinting technique that seems to be popular in types of photography such as weddings, where a tree in the background is made to appear more vividly green than it actually is?

Would this involve additional software or could the results be achieved in say Photoshop or PSP?, I presume that this sort of colour enhancement(if i have understood the term cel shading correctly) cannot be achieved from within the poser material room..........I further presume it would involve creating your image in a series of transparent background images....