Well, with just a little way to go in "American Gods," here's what I noticed in my reading:
- When Shadow's watching his own mother's death when he was a kid, he sees his younger self with "acne pocking his cream-and-coffee skin". Also his mom's got sickle-cell disease, which is far more common among people with African heritage, although that by itself doesn't prove anything, of course.
- On the other hand, Whiskey Jack describes Shadow and Wednesday as "two white men." Maybe "white" is his generic term for non-Native American.
- But on the other hand, when Shadow and Sam first meet and Sam tells him "White people have some fucked-up gods," I took that to mean "white people as distinct from you and me".
Overall, going mostly on that "cream-and-coffee skin", I'd say Shadow's mixed-race with some African heritage mixed in there. Sure he has one totally white parent, but so does Barack Obama.