Over annealed sterling turning fingers green

Hi there! I have sterling rings (plain bands) that my manufacturer annealed for me so they are soft for stamping. A few of my customers have complained that the rings are turning their fingers green :grimacing: Do you think this is due to copper oxides brought to the surface when annealing? Maybe they “over” annealed? If so, would pickling them help? Also, would annealing at a lower temperature for longer be a better option?
Thanks for your help!!!