But I doubt he was ever listed as anything other than white in census records.
The census taker didn't ask for someone to trot out their pedigree chart (even if they had one). They went by observation.
If someone was consistently listed as mulatto in every census record they appear in - more than likely they were not white and could not pass as white. That is not to say the census takers were always accurate or thorough in their work. I found one Confederate soldier listed in various records dating from 1850 to 1900 as -believe it or no- white, black, mulatto and octoroon.
In Gibson's case, it was being pointed out that as a person of sufficient black descent to be a slave, he should not be a general. He did some research to his great grandfather owning a plantation - that's it, he was white, blacks can't own that. However...ONE more generation and he would have found his great great grandfather was a free black who did indeed own the plantation.
Race designation is interesting, especially to the Native population. As you say - depended on what you looked like. If you were very dark, Negro would be on your birth certificate. If you were very light, white would be put down. I have a Confederate ancestor from the Catawba of South Carolina - he enlisted as 'colored', got shot at Gettysburg and sent home...and was re-enlisted 'white'! Guess he was indoors a lot recuperating... I believe you when you say people observing who you are by your looks may not get it right - at all.
