Thanks. I think this occured after a viewing of Secret of Nihm with my kids.
If you go in-depth with the 'ratling' race, you may have the colors correspond to castes, or possibly determine some class preference (Black rogues, Brown Ranger/Warriors, Albino Spellcasters, etc), or you could just make them different factions that don't really get along if you are trying to add a little political dialog to the area.
Personally, I would just go with different colors to break the monotomy of the area, using the ratlings as additional filler. Let the players think there is some mystery behind the colors, when there likely is none. Players are as likely to just want to move on to better paying regions, leaving Region A behind - so I would not put huge creative effort into the first region of the massive dungeon.