Granted I'm only lvl 55 in this class, but so far the white/black bar casting to me feels like needless complication since it all pertains to just dps. The spells are about the same dps-wise, so essentially it can all be reduced to just a 200 pool of resource of either the verthunder or veraero as the nuke. It's all virtually arbitrary since they just take one nuke spell, call the same thing with two different names to spit the white/black magic labels on it.
Not even the cure spell screws up the white bar which I kinda wish it would to make it more challenging to manage the resources.
Going in newb, I thought the system would have been more like: all utility spells such as cure, protect, raise, i.e. -> white mage stuff gives white resource, and all nuke spells/enchant sword with fire stuff i.e. -> black mage stuff gives black resource, and each can be spent on either a black uber spell or white uber spell every once in awhile. With a few special/blended spells here and there that require both (like give an aoe damage and aoe heal all at once that require resource of each).
As of now the white and black magic spells you cast to gain resource have no separate roles in it and kinda a shitty design...