Actually you have to ask Mistra's assistant Pharell at Atlantis to exchange for green set gear.

Show Quest Info

Introduction

Nobody knows why Mistra at Atlantis owns so much green gear, but nobody really cares much either. What's important is that you might be able to get some from him. Mistra is a stingy fellow, and won't just give you the gear... You'll have to do something for him first.

NPC Dialog

I do indeed have a lot of green gear, but if you want some of it, you'll have to do something for me first. Finish the five quests I give you, and you'll receive a Stamp of Promotion. You can trade these with my assistant Pharell for green gear. She's that beautiful lady over yonder.

Quest Completion

Hello, you! I am Mistra's assistant. People say I am a beauty, that makes me really happy.