SSP yellow on their back, can they be cleaned up?

[Lili4ka]

Hello,

I saw this pair of pre-owned ssp earrings on ebay. They look partially yellow - is that possible?
Would that be dirt that can be cleaned? what do you think?

http://www.ebay.com/itm/171993169537?_trksid=p2055119.m1438.l2649&ssPageName=STRK:MEBIDX:IT

 

[jshepherd]

That appears to be the color of the pearls, not residue. Yes, it is possible to have natural yellowing and it would be permanent.