The Negative Superman was a copy of Superman created using a ray-gun. His color scheme was black and white, including his costume and face, and he and Superman repel each other like two magnets.
The Negative Superman was created when a villain intended to turn Superman ghostly with a new ray gun, but instead created a negative copy of him. ("The Negative Superman!")
Alt Baltazar Continuity
The Negative Superman was created by Red Kryptonite rays which Titano was shooting out of his eyes after being transformed into a giant gorilla by drinking Kryptonite coffee. His secret identity name was Clark Kant, the last name being a negative spin on 'Kent'. He attempted to ruin Superman's reputation, but Superman defeated him. (Superman Family Adventures #4)