What Causes Pink Discoloration Of Ornaments Worn On Skin?

Hello Doctor,
My question is regarding my skin. i am wearing a black beads necklace of a white silk thread and now the white thread is turning into a pink colour as well as my white slippers are also turning into a pink..and before also i was wearing slippers of different company and it too turned pink..now i want to know why its happening? please send me the answer..thank you