Not an easy undertaking by any means. Do you want to do direct modifications to your system? This is really something that is a high level of difficulty with the potential of completely bricking your system. Not that it can't be done.
If you are trying for separate colors in different layers like my D&D Dice Jail lid, then it is a simple matter of adding a pause to the print (not too hard in Cura).
If you want true multi-color printing, you either need to butcher your system (replace the current extruder with a dual feed, add wiring for the new extruder, modify the firmware, and pray you don't screw it up) or you could buy something like the
Mosaic Pallete 2 and be up and running in no time.