Spoiler warning: Quest and/or game spoiling details follow.
Irmana (Venore) trades a Red Robe for a Red Piece of Cloth.
A Red Piece of Cloth can be given to NPC Cael (Farmine) in exchange for a Dragon Throne after handing in 12 Tomes of Knowledge.
50 of these are needed for the Barbarian Outfits Quest.
50 of these are needed for the Assassin Outfits Quest.
20 of these are needed for the male Summoner Outfits Quest / female Mage Outfits Quest.
1 of these are needed for the Jester Outfits Quest.
Spoiler ends here.