I can see how the odds of fraternal twins being born like that can be a million in one if you figire on the statistics of a interacial marriage times the statistics of fraternal twins times the statistics of one being lighter and the other being darker (which is how you determine the probability of multiple statistics). On the other hand, I know a few people who are in interacial relationships that have children who have blond hair, blue eyes, fair skin and their siblings are dark hair, tan skin, and brown eyes. You just never know!
My SIL (half Tanzanian, half German) and my brother (we're American of mixed European descent: English, Irish, German, Swedish, etc...) have 3 children: the first two have the exact same ultra white skin that my brother and I have (the first child has red hair, the second child has blond hair), and the third has the exact same brown skin that my SIL has (and dark hair).
Wow that's so cool! They really don't look like they are related at all. The one has curly hair and the other has straight hair, and the shape of their eyes and everything.
My oldest has skin color exactly between dh and I. Her little sister was born much lighter but has darkened to the same color as my oldest this past year. My MIL says babies don't often find their true color until they are about 3 years old.