Your argument is good, but further research shows that John Hanson could have had a close Black ancestor without someone’s misuse of the John Hanson photo taken in the mid 19th Century. A quick Wikipedia search showed this information.

Hanson was of African descent
Main article: African-American heritage of United States presidents
Dick Gregory, comedian and African-American activist, publishes an on-line column called Global Watch. In one of his columns he repeated most of the myths and added a new one, that John Hanson was the descendant of an African American.[8]
There are two possible origins for this belief. The first is that Hanson’s grandfather, another John Hanson, was an early English immigrant to Maryland. As was common at the time, he worked as an indentured servant on his arrival in the New World to pay off the cost of his passage. In 1661, his first master, William Plumley, sold his contract to Edward Keene and recorded the contract with the court of Calvert County, Maryland; similar court records were also used to transfer title to land and slaves. But, in six years, the immigrant John Hanson had worked his way out of debt. A few years later, he purchased his own small farm. There is no record that the grandfather was black, but the record of sale of the indenture contract may have been confused by researchers with that of chattel slavery.

Then check out this link. http://en.wikipedia.org/wiki/African-American_heritage_of_United_States_presidents

So I have found two holes in your argument. One, that John Hanson’s grandfather’s name was also John Hanson and that there is no record that the grandfather was Black, which can be translated to this conclusion. Any mixup between two John Hansons are probably with the President of the Continental Congress and his grandfather, not the Black Liberian Senator. And there is no record saying John Hanson is white either.

The above link also shows that it was possible during this country’s early history for an individual of one quarter or eigth African ancestry to be accepted in the white world and achieve such status. So that’s another flaw in your argument. Maybe I will tackle the other alleged Black tale.

Logical Historian