So yes, black mages often can be evil. But black as a color is not inherently evil. Being influenced by black’s philosophies does not necessarily mean that one will commit an evil act. That being the case, we cannot say that black represents evil. More closely aligned with evil than the other colors? Fine. More ripe with potential for evil? Sure. Evil? No. And that's a very important distinction
Mark Rosewater, Magic: The Gathering -- Official Encyclopedia, Volume 2: The Complete Card Guide
color, dark, evil, magic