I'm the anon who replied to OP right below you, and that's how I felt too. Shadow's personality was so bland that his race made no impression on me whatsoever. If you told me he was supposed to be black, ok. Asian, ok. White? Ok.

If someone asked me, I'd have guessed white but only because the author is white too and I'd assume a white guy would write a white guy, and not because of "Shadow" the character at all. But then I generally don't bothers to imagine book characters' physical features unless they make a difference, which they didn't.