These blue robes are the signature clothing worn by every respectable mage. Apprentices look forward to the day they first wear these, as it shows they have graduated to full wizard status. The wizard's tower, in particular, uses these robes as a uniform, signifying their magical power and fealty to the god of order, Saradomin.
All documents have been expunged of the events that came to be known as the Day of Purple Feathers. No wizard or knight will speak of what occurred. However, villagers soon learned that squawking like a chicken would send both knight and wizard into unexplained panic.
For some reason, the egg deliveries to the Wizard's guild were cancelled around the same time.