Have you read "Tales From The Vulgar Unicorn?" The original Blue Mage is one of the PoV characters. Later volumes deal with many aspects of being a Blue Mage, including the organization behind them.

One aspect I like is their major disability: each Blue Mage has a secret, the revelation of which permanently strips them of their power.

As a DM I might rule that revealing the secret forces the mage to dismiss all active spells and require a full rest before being able to cast again. This secret should be one worth hiding as opposed to something which is in effect nothing more than a trigger for a spell effect. So, for example, a person who betrayed his family to gain power has something to hide, while having the character's name said backwards is a trigger, but has no relevance to the character.

For PCs, the permanent loss of spellcasting ability is a severe penalty. This is why I advocate the temporary loss of power. However, should a Blue Mage's secret become commonly known the mage will effectively become useless. In this case I advocate a quest to return to the college of Blue Magi to be granted another secret.