well the first simple reason i was thinking of for the Glukkons' difference in skin color is that it would be boring to see all os them in one color. there are so many important Glukkon personell which the player needs to destinguish from each other. therefore, this may seem to make sense.
but if we look at it OW wise, my only problem with the chemical solution (of snuzi, i think) is that it isnt only the skin color that differs between red and green Glukkons. its the shape of their heads and face. green ones like Brewmaster or Tex the Glockstar at the auction tend to have larger eyes and narrower heads. (by the way an interesting thing: did anyone notice that in the MO good ending movie Tex the Glockstar does not have ears?? :S i looked hard many times since than but he still havent grown any
)
look at these two pics for comparison: