theres no telling and even if born one colour it may change.
I have brown hair, my partner has brown too. My son was born with masses of black hair which fell out and grew back blonde. My daughter was born with black hair and that is fading slowly to a lovely reddish brown.
My husband and I both have dark brown hair, but I was blond until I was about 11. My elder son has medium brown hair and my younger a dark blond. My mum and dad both had brown hair and had 7 kids.1 red, 2 strawberry blond, 1 blond, 1 very dark brown - almost black, 1 dark brown, and 1 mousy - so you just never can tell!!!!
it might depend on what is the recessive and dominant genes, i can't remember which is the stronger gene, but depending how many genes of each colour the baby gets will probably determine what colour the baby has. e.g. if the baby has 3 blonde genes and one brown gene then chances are the baby will be blonde. so you'll never know!