My specific question to Griff is whether or not black magic corruption is Outsider corruption. I ask this because I believe Harry was corrupted by black magic. If a starborn is immune to Outsider corruption, then Harry would be immune from black magic corruption if it was Outsider corruption.
Harry isn't immune from black magic corruption, therefore black magic corruption isn't Outsider corruption. (At least that's my thinking assuming starborn are immune to Outsider corruption).
Now it could be that starborn have really strong resistance, not immunity, to Outsider corruption. This would explain why Harry didn't go full warlock from his corruption and why borderline 1st Law violations don't seem to have any affect on him. Killing the Turtlenecks with magic might make a regular wizard go full on cackling evil. But for Harry, it's no big deal. (Or they're not 1st Law violations at all). I'd have to carefully parse what Eb said in PT about it.
I think magic a spectrum of energy, with different types of magic working at different frequencies.
I think Outsider magic (spells, incantations) is on a specific frequency that goes Outside. I think the Outsider frequency is in the dark end of the spectrum, so it's dark magic, but not the same as other dark magics. Hellfire is a dark magic, but it's a different frequency.
Likewise, faith magic, soulfire, and other examples that we don't see much of are light magic.
I think mortal magic is unique because it's basically neutral, but the intent and the result can both change the frequency. If Harry casts fire to light a candle, it's not dark. If he does it to kill someone, or he inadvertently kills someone with it, then a spiritual backlash occurs that taints it as dark. That pain and suffering that his magic causes splashes back on his magic/aura/spirit/soul, and it stains it.
It's easier to picture it as paint. If every mortal starts off with a gray base paint, then how they use their magic will affect the color. Do something dark, like killing someone, and you're going to get a splash of black in that gray. Use your power for good, like making a baby laugh, and you're going to get a splash of white. And since every type of black magic is its own color/frequency, it can be distinguished from others.
Likewise, if you come into contact with magic that's dark enough, and it comes into contact with your spirit/paintcan, then stains can be left even without your involvement.