Does anyone have any insight re: how the census takers were instructed to record race. I've noticed that a few of my family members are listed as 'mulatto' on early records and then listed as 'black' on later census records.

Also, in one line has everyone in the family listed as mulatto, except one child.

1880 Census
John (m, head)
Mary (m, wife)
* robert (b, oldest son) * ????
- lucy (m, daughter)
- chas n (m, son)
- john k (m, son)
Lucy (m, grandmother)

I Am curious ... does this imply that the father had a child by another woman or that the census taker assigns race by 'appearance'/skin color ... or is there some other reason?

Also, the same Chas N listed above is listed as Negro on the 1930 census.