Some magical beings can cleanse their auras with a spell. Paige Matthews saw her grandmother Penny Halliwell cleanse her aura in the sixties after accidentally traveling back in time. Paige also mentioned there was an Aura Cleansing spell in the Book of Shadows.
Some magical beings can persuade people in order to manipulate and corrupt them. When the Source of All Evil manipulated Paige Matthews into attempting to kill a suspected abusive father, her aura turned black.
The ability to choke beings with their own aura. This is the main offensive power of Grimlocks, who choke their victims by reaching out and then squeezing their hands into fists. The victims then feel their aura tightening around their throat and they start to suffocate.