In concept art, his hair is either black, brown or blonde.

He was born with blonde hair but dove into an ink like substance to hide. His hair begun to go brown but became black hours later. Also turning his skin grey. He tried to clean off the grey color but could only have pure white.

Sloth's pool of healing cleans off the effects, so he can look normal again.

He dives into the ink more to conceal his identity because of anyone who could know him.

It's not ink but corrupted magic of Cerin, god of darkness.