For people like that I would be comfortable hoping that their child would come out the EXACT opposite of they wanted, no matter who who they mated with.
You just never know. My grandmother is light as a bulb, and my mother came out dark skinned, looking like my great grandma Chief. Anyone getting with my grandmother hoping the child would come out giving a "mixed" mess out would have disappointed. My uncle (her brother) is also dark skinned. The same tone as me. My aunt is the ONLY one in my immediate family who is very light skinned like my grandmother.

DNA is very random with its selection at times.
But then my concern would be the psychological welfare of the child -- having a parent who is disappointed with them from birth. So I'll hope these idiots get what they want.