Some red wizard (I don't get it, he is wearing green) is after Edwin. He turned Edwin back into a man, and we killed the Red wizard. Why are the Red (green) Wizards after Edwin? Is there a quest here, or did it end when I killed the wizard dude?

Have you done Edwins quest with the Tome yet? If so, this should happen.

no, I mean after you kill the red(green) wizard dude, does anything happen in Edwin's quest? I already gote the nether scroll, if that's what you mean. The red(green) wizard changed edwin back into a man.

Nothing else happens in Edwins quest when he is restored to normal.
I guess that the Red Wizard was wearing green since in Amn wizard aren't really welcome and Red Wizards even less.