I will be honest and say that because, in terms of the larger setting and the rules of magic in this setting, that's simply not how I want it to work. The setting wasn't made for this RP, this RP was made because I thought people might enjoy the setting. One of the rules I have had in mind for the setting for a long time is that Necromancy was a colorless magic with no association to any affinity, for much the same reason that all onmyouji are capable of performing exorcisms.

It's not learning outside of your affinity because it has no affinity.

I suppose a list of unacceptable affinities could be arranged, though off the top of my head it's really just "Mana, Death, and anything that is an entire class of beings".