Is my hair a dominant allele?

My father was blond as a kid, but over the years his hair slowly turned black. My mom has light brown hair. I was blond as a kid also, but my hair turned dark as well. it's not fully black yet, but it's getting there. My dad had another kid, but i don't know her so i can't tell if she has his hair too. Like most people, i want my kids to look like me. though i am attracted to all kinds of women, blondes seem to catch my eye the most. my question is, if i had a kid with a blonde girl, what color would its hair be?