> - One is a slur based strictly on the color of one's skin
I've talked to far-right people who would dispute that. They'd say there's a difference between a black man and a n., and you can be a n. if you're white, because it's the behavior that defines it.
> - One is a slur based on one's sexual preferences
That one is even more questionable, I believe. Effeminate men are called f., especially homosexuals. Nobody calls a bear that. Sissy would be a similar term, and it's used in similar ways as a pejorative towards heterosexual men when they act "unmanly" in the same way.
> One is a slur based on a self-applied label
As was mentioned: it is not always self-applied, especially not when used as a slur, where the usage has reached inflationary levels on e.g. imgur.