Versace Medusa 18” chain

This Versace necklace was purchased from the Versace store in Houston at the Galleria Mall. I only wore it a handful of times and kept it stored in the box. When I went to wear it recently, I noticed the necklace had a darkened color. At first I thought I would send it to be re-plated somewhere because I love it so much. I paid $1350 w/ tax. I have decided to sell it. I never tried to clean it. I think someone out there with the means to fix it will get a good deal out of it. Thank you!!