Dead Beat:
-Wizard healing/longevity are introduced.
-Both Evil Bob and Grevane refer to necromancy as "The True Magic". It is different enough from normal magic that it stains the user. Grevane (and Ulsharavas from DM) can sense it in Harry. Harry can sense it in Cowl.
I think we're dealing with two different types of magic here, each with two variations. There's normal magic, "the magic of life," which comes from all living things. This can be corrupted into black magic, which Harry hates and to which he reacts badly. Then there's necromantic magic, or, I suppose, "the magic of death," which is Grevane's magic, and which is what(I believe) he and Evil Bob were referring to as "the true magic."
Then, lastly, there is what Kumori did with that random dead guy on the street in
Dead Beat. She warded his soul into his body somehow to prevent him from dying. Harry noted that the coldness of necromancy was there on the scene, but that it didn't have the sense of corruption to it that usually came along with the coldness of necromancy. And Kumori herself said that she had basically perverted necromancy into serving life, sort of the way normal magic can be perverted into destroying life as black magic.
So, there's normal magic and necromantic magic, and each one can be used either to serve life or to destroy it. Kumori said that one's purpose had to be strong to use necromancy in the service of life, though, which would seem to indicate that it's easier to use necromancy for destruction than for preservation. When normal magic is used for destruction-- I think this is the typical form of black magic that's shown in the books, the stuff that sorcerers are good at. Necromancy is usually used as black magic, though, and until Harry saw the signs of Kumori's spell in DB, he apparently didn't even think it could be used for anything other than black magic.
And, I guess, the stuff that Outsiders do is some other form of magic altogether. Unrelated to normal magic or necromancy, I'm guessing.
This is all conjecture on my part, though, put together from the various pieces of information in the books. I don't have any solid evidence that things work exactly this way, except that this description seems to fit with all of the information we've been given over the course of the series.