You can see his roots in the photo above. Mark Hamil before sun bleached:

cough edit: you will also find that in return of the jedi he has brown hair meaning as he aged his hair got darker this is pretty normal in people who’s parents have brown/black hair

C’mon man… Learn genetics. Seriously. Recessive genes can ABSOLUTELY express themselves in a child from even one parent being a carrier regardless of how the parents’ genes express. In addition, random mutations can and DO produce weird things.

He lives and works in the fucking desert - his hair is sun bleached.