Actually, there was a heated debate as to what the shorthand for Blue Mage was going to be (BUM, BLU, BMG, etc.) and I think the most recent interview confirmed that it was going to be "BLU".

No one is really sure how BLU will play out, but if you're just starting the game, you'll need to get to level 30 before you can access the quest for this advanced job. Well, at least I think it's 30. How funny it would be if Square decided to change the level requirement for this specific job to something like 50. But either way, you can bet that a whole mess of people are going to jump on this job the minute it's available. I can't wait to see how the dunes are going to be with all these people seeking as BLU.