If the baby is not an albino then I would think it is pretty uncommon. Although I have seen several cases recently where a mixed race couple has given birth to a child that looks to be "white."
Several years back there was a mixed couple in Britain that had a set of fraternal twins where one was white and the other appeared to be the same color as the parents.
I don't know if I can post a link, but Snopes has pictures of the twins in Britain.
http://www.snopes.com/photos/people/mixedtwins.asp