I am not one to bad mouth someone else's work so I would never have brought up about the dark bases but since it already has been mentioned I will comment.
Whoever did your mount most definitely boiled it and they did not take any precautions to protect the antlers to keep them from darkening. Even if you boil skulls there are techniques that can be used to keep the antlers from turning dark.
If you like it and are okay with it then nothing else matters. Enjoy it.
If you don't care for the dark antlers, then if you are ever around my way, stop and see me. I know of a method to return them close to the way they looked before they were darkened.