I agree that some developers seem to be like that. The same black worg, grey worm, black buzzard, etc. over and over again, and probably because they did just copy it from another zone for convenience, as adding variety/rare colours isn't high on their priority list as long as the zone is populated.
But if you look at the list of skins that were on the untameable list, but have been made tameable in this beta, it's obvious that some developers are going out of their way to add more colours. The list is now huge. Every last parrot skin bar one, all the bone spiders, all but one warp stalker, the missing aether ray, serpent and scorpid skins. So we have someone to thank, and hopefully they'll add more before this expansion is released