The thing with blue magic is that a handful of spells are very good (white wind, mighty guard, when they don't have atrocious casting times), but the rest sort of gathers dust.

White magic tends to be useful throughout the game, gets regular upgrades, and most of their spells are useful. Black magic the same. Blue mages tend to play as esoteric red mages, with some good healing spells, variable elemental spells and the odd status effect spell. It all depends on the game, really. Some blue magic is better than others.