So skin tone covers a skin detail - Tail/Ears

So I was wondering what you have to do to be able to cover an item that is located in Skin Details, in this case ears and tails, so that the overall fur skin tone you are using on the sim covers them. Currently they just add black. I have other downloaded ears that take on the skin tone but I am not sure how they do that. I tried to look and see in Sims Studio what was missing or needed for it, but I can't find the answer. 

Any ideas/instruction would be most welcome! :D