They are the cubic zirconia inside the 10 karat gold
That get green on you, when you get green on 'em

from Kanye West – Gossip Files Lyrics on Rap Genius

Cubic zirconia is extremely cheap, and is known as the knockoff version of diamond. With most jewelry made from cubic zirconia, brass is also used in the structure of the product. The copper from the brass will eventually wear off and turn your skin green.
Additionally, people always seem to get green with envy when you start making money

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