I looked up Henry on Ancestry.com, having a few Stewarts in my tree. His WWI registration there has "white" checked even though there is a spot for Indians. It did note he had black hair and eyes, but so did my dad and his dad even though the last Indian in that line was in the early 1600s. His death certificate also states "white." WWII registration and wedding cert are on there, too, but don't have that information.
For party information, you might ask the county Rep. offices where he lived if they have any rosters or records of committee members. If he didn't hold an office, the county central committee might have been where he took part.
Good luck with your efforts.