This occurrence is not impossible though. There are already some previous cases of twins with different skin colors and different fathers.

Naa gani to murag artificial insemination gani ang pag-conceive sa baby tapos ang one twin kay lain ug color kay naay mix up sa sperm adto sa lab.
wa lang.
DNA Paternity Test Reveals Twins With Different Fathers
There is such a thing as bi-paternal twins.

It's extremely rare that's why it's so cool. lol. from dnacenter.com which should be quite credible, dontchathink? hehe