When you're in the Blue Mage class, you have to get hit by a Blue Magic spell. The "Learning" ability is only if you switch out of Blue Mage class and still want to learn Blue Magic. Either way, you have to be hit by the spell and survive (so if there are any instant death Blue Magics in this one, I can't remember if there are or not, you have to protect the character against death before they get hit by it).