How do I color the shading of a material? Some art styles increase the saturation in their shading, I'm trying to achieve this effect as seen in cell #2 of my example image. Right now it looks like cell #3, which lacks this and looks dull in the render.



I just have #1 as a default frame of reference, and #4 is an exaggeration of the effect I want; using color for darker areas instead of just darkening. If I could achieve the effect in cell #4, I could easily change it to be like cell #2.

So far I have tried creating 2 material nodes with one of them inverted, and then mixing them. This doesn't show in render mode, and it still doesn't let me change the color where needed. I'm not sure how to go about creating the effect shown in cell #2, because I'm quite new to nodes.
This is something you can do very easily in the Blender Internal renderer, where, unlike Cycles, you can feed the output of light's interaction with a surface back into the calculation. 

In Cycles, this would lead to a feedback loop: (lighting affects surface affects lighting affects....), so there, you would have break the loop by baking the outcome of one light/surface interaction as, say, a diffuse texture,  and use it to influence a  second.

Simplest sort of node setup:



(You can use the shading output any way you like)

Result..



In Cycles, you could find a more physically-based route to a specific effect you were looking for .. perhaps subsurface scattering, translucency, fresnel...