What is coles evil twin called in charmed?

Cole doesn't have an evil twin. So I can assume you mean either one of two things.

# Cole's demonic half is called Belthazor He's mostly red with black stripes. or

2. In the season 4 episode "As Black as Cole" there was demon who was reverse colors of Belthazor named Sykes. He was half-human, half-demon like Cole, only he wasn't "good" like Cole was trying to be.