After you have unlocked the giant monolith at Lohgrin.
Go to Pendrago and talk to the men near the entrance, he will say something about a new poem from Mayvin. Now go to Lohgrin, and talk to another man near the inn who will talk about Mayvin.
Go to Trizolde Cave, you should see “!” on the map. Talk to the girl and you will get the Shepherd’s Outfit: Alt. Color.