Her name is Rosario sounds of Spanish descent. Let me check the.. yep. No African here (well let's say, 1/64th ;):
From Rosario's trivia page
Rosario was raised in Manhattan. Rosario's mother, Isabel Celeste, is a writer and professional vocalist, who has Puerto Rican and Afro-Cuban ancestry. Rosario's biological father's name is Patrick C. Harris. Rosario's mother married Greg Dawson, a caucasian construction worker who raised Rosario and gave her his surname.
I know that doesn't add to the answer to your Q, however. I was trying to find a snapshot of that scene on google images and couldn't come up with one. I thought I saw an asian girl because I see them everywhere, was Laurana really asian?
EDIT: YEP, she definitely looks asian but she is an alien so do they have asians? Maybe on her planet she is actually puerto rican
Couldn't find a decent pic, so I made one:
http://i61.tinypic.com/laz29.jpg

"Your wife's on my Wham-O"

the writers could easily explain that saying she was alien and somehow that's what happens when they reproduce