Expanding Map Capabilities (and realism)

I am making a new mod component that will change the way maps get created. (Actually it will add to the current way). It will also include some new layers to view on the map.

I need someone to point to where I can figure out where the map is colored or changes according to one is viewing. I believe its somewhere in the python code but can't find it as of yet. I also need this before I can start programming it because I need to be able to color the map according to CvAreas. I need a different color for each area in order to see how area defines work.

Can anyone help point out where this functionality is?