I have always thought my great grandmother, Nancy Jane Seaver, looked to be something other than European, as do photos of her mother, Sarah Cline Seaver.
I have little evidence to confirm my hypothosis, but I believe the Seaver/Crobergers were possibly Melungeons. This unique mix of European, Native American, and African ancestry was known to live in Northeastern Tennessee and Scott County, Virginia, as did the Seavers and Crobergers.
There are several unrecognized small tribes from the area that intermarried with each other, and possibly free African immigrants or escaped slaves. They sometimes referred to themselves as Cherokee, which was far more socially acceptable at the time. When the Cherokee et al were driven from Tennessee in the 1830's, they simply claimed to be white if they could "pass" and other claimed to be Portugese.
Some think Abe Lincoln was of Melungeon descent, from his mother's (Hanks) side. His dark features, nose, and skin look very much like my great grandmother's (a Seaver.) There's no link between them, he is simply an example of Melungeon features.
Thus far, this is only speculation based on circumstantial evidence. But I think were question is definitely worth asking.