An item, pehaps a decor like Tigers Eye, which hides the mutation on adult lions. The lion is still genetically a mutie and can pass it, if applicable, (Primals, Piebald, Dwarf) but the appearance is changed to the default form.
For example, I can see it being used when you prefer the non-mutie art on your king but still want him to pass Primal or Piebald genetically, or maybe if you just want a change! It should be reversable as well. It would be nice to give more options to customizing your lions. :)