Robes of the Lich

This item drops from Amnennar the Coldbringer in Razorfen Downs.

Speculation
They could be a reference to Kel'thuzad, who was once a high ranking member of the Kirin Tor, and who later became a Lich, hence the violet colouring referencing his own robes. This could also go for any Lich who was a former Kirin Tor Mage, perhaps most likely of them all being the Lich who drops them, himself, the Coldbringer.