User blog comment:Lord Loss/Monster Hunter Theory... Blog/@comment-1758220-20130422062858/@comment-4009941-20130504221228

Eye color could just be different because its a alternate eye color in the species not all creatures of the same species have the same eye color, us for a easy example.

And as far as DNA change mentioned above, last I checked evolution would suggest DNA changing anyway? Green Narga could be a minor change in the species as far its tail is. Also maybe it eats something normal Narga don't, or maybe the tail spikes are just a minor change making it a actual Subspecies.