In another post, http://www.pearl-guide.com/forum/showthread.php?t=56 someone asked about black Mexican pearls. J Shepherd responded and said there are black Mexican pearls.
I googled Mexican pearls and found this site with a brief history.
Balboa christened the Pacific ocean on the sw side of Mexico the Mar de Sur and the first South Sea pearls were from the Gulf of California. Click through for some interesting history and interesting pictures.
Looks like a growth industry and we are among the first to hear about it!