What I want to do is adjust the parameters of a shader based of the intensity of light being received. The main thing is saturation. Often in a photo, parts of an object in bright direct light look unsaturated and parts in darkness look a more saturated. Ray tracers like VRay appear to do the opposite, making very bright areas saturated and dark areas less saturated. I realise that I could adjust this using the 'rawLight' pass in post but I would much prefer to do this in render. Does anyone have any ideas on how to do this?

While my general interest is being able to do this with any shader, my particular interest is in a scene involving SSS that I'm working on at the moment.

Have a look at this image:
http://i.istockimg.com/file_thumbview_approve/16665303/2/stock-photo-16665303-sushi-plate.jpg

See how the part of the salmon that's in shadow is a much deeper red. When I try an recreate this in VRay using the SSS2 shader, the side of the piece of fish looks more grey, even a little green.

Another problem I'm having is getting the rice to receive colour bleeding from the fish. I'm using brute force primary and secondary bounces. At the moment the part of the rice that is shaded by the fish is grey whereas in the photo it is definitely an orangey colour.

Any help with this would really be appreciated,

Thanks :)