I don't know the answer, but I just scoured my copy of the book, The Pink Pearl, to see if there were any references to treatments. I didn't find anything about treatments but I did find this:
"Some of the non-pink colours, such as 'golden' orange-yellow, 'milk chocolate' brown and pure white are very rarely found unblemished, but when they are, they can be true collector's items, fetching high prices."
(p. 65)
Opposite that page, on p. 64, is a color plate showing an assortment of pearls; lots of them had spots or other variability in color.
Personally I would not try to remove what you are calling discoloration....