Did you find a marriage for John in Oklahoma? If you found that you can see what year it was and you can look for them on a census. It is true that the census takers often made assumptions based on looks and sometimes the neighbors gave the information if the family wasn't home. My husband's grandmother and siblings are listed as Cherokee/Mixed as adults on ONE census but their is no proof whatsoever and they were listed as white other times. Their parents were always listed as white. Living in Oklahoma I often see that and everyone says they have Native American ancestry. You really have to have a relative with a roll number that kept it going from generation to generation to be sure unless you get really lucky and can find them when they had their Indian names and white names listed. If you can find the names then you can look on the final rolls.