Thank you for all your responses to my last post regarding the use of black pearls in the Tudor era.  As seekatesew  and myladyswardrobe  pointed out, it was most likely that the 19th century touch-up of the Holbein sketch darkened the pearls, and that the original was probably white pearls.



I believe this is the sketch that the print was based on, and indeed the 19th century version did employ artistic license with the pearl decoration. 

Case closed!  :)