I Dont undertstand how i got my hair color!?

Well you see im indina and its weird for indians too have dark brown hair, its pretty dark and u can see it in the light and both of my parents have black hair and so does my brother. And i found out the alleles for my parents so i could use it on a punnet square and my dads is Bb (B-black and b-brown) and my mom being BB (black) and i did the punnet square and everything on it ended up that i would have too have black hair but i dont understand how i ended up wit dark brown. And wen i asked my dad he said my grandma had dark brown hair so i hope that information helps.