Could be on their genes anyway, from a grandpa, grandma. I didn't mention that with the Simpsons cause we've seen their other family and none are blonde
My parents both have light brown hair and my sisters and I have the whole spectrum... Dark, brown, redhead, blond. It's not like it's impossible =) even if you don't see your hair color in your relatives, recessive stains can still appear it just may be less likely
Find out who you are
You got to dig a little deeper
It really ain't that far
(Not implying it's just a possibility)