There is a long discussion in VV2 genetics started by Complexity which should answer all your questions. Basically, if you can imagine all hair colors in a line from darkest to lightest, then your child will fall somewhere between the two parents. If you have no redheads or blondes, getting a redhead maybe a little harder but not impossible. There are some other possibilities here, too. Sometimes a child is born who is way out of the expected range of colors from the parents. And there are events which can change a villagers' appearance.
I like redheads too. So Good Luck!