It's pretty straightforward there. His parents are opposites, fell in love and did a Romeo and Juliet and faked their own deaths to be together, but they didn't think having a kid would be a bad idea until he started randomly changing from dark tones, brooding and quiet to blonde and sweet, using both sides of the spectrum on either transformation.
Oh he already knows why. He was born with equal and yet vying sides of light magic and dark magic. His first transformation happened when he was four years old, from light to dark, and before puberty he had a head of half black and half pale blonde hair, until it evened out into one or the other specifically.