It's a cultured freshwater pearl from China and that is the natural color.
These kinds of fancy shapes (stars, coins, crosses etc.) form when a specially shaped nucleus is placed inside an already existing pearl sac and the mussel is returned to the water. The pearl sac secretes nacre to cover the shaped nucleus.
But you may wonder, where did the original pearl sac come from? The pearl sac formed originally when a bit of mantle tissue from a donor mussel was placed in the mantle tissue of a host mussel. The donor mantle tissue forms the pearl sac. The result of that is a solid nacre freshwater pearl, most often potato shaped or baroque, but sometimes nearly round. That's the first harvest pearl.
The shaped pearl is the second harvest pearl.