So far, I've found a bunch of grey, two blue and two yellow/gold items. This page talks about 4 levels of rarity: normal, magic, rare and unique. But there are no information about the colors. My guess:
- grey = normal,
- blue = magic,
- gold = rare,
- ???? = unique
Also, I couldn't find a "pattern" of increasing currency while selling items to the PNJ's. For example, I sold a normal bow, the PNJ gave me two pieces of scroll (wisdom). Then I sold a magic bow and received... two pieces of scroll (wisdom). Maybe the magic bow was a really weak one ?