I wish there was a way to color vary pops procedurally, and did a lot of testing to find it. To no avail. It could work if only PF's could be projected from a camera. But the only thing to be projected from a camera is an image mask, as far as I found out. There must be other ways, but that would be up to Planetside to implement, I guess.
Anyway, in short: Make a square, patchy and colourful PS image (such as attached), load in image map shader, set to repeat. Attach a new camera, locate this over your population, and set rotation to -90/0/0. You can play with the FOV angle. Perhaps orthographic would work, I never tried.
To test, attach this to a color input of a surface shader, and raise height according to what you see.
Now open your pop, get to the object internals and attach a new surface shader between the two shaders (default and the other one). If there are more internal shaders, repeat this or just take a few. Find the image map shader in the color input (there are more possibilities there), and work with the coverage until it works fine.
---Dune