Loving V Virginia was a Supreme Court case in 1967 deciding that there can be no law against mixed race marriages. The Virginia law had language specifying a person classified as "white" could not marry a person classified as "colored". Does this mean that marriages where neither party was white were legal. Were non white mixed marriages more acceptable?
I know that the Siamese twins Chang and Eng Bunker had problems when they moved to North Carolina with attempts to classify their race. Eventually, they must have been considered white as they were married to white people and owned slaves. Their descendants (they managed to have about 23 children) ignored the "one-drop" rule that applied to African ancestry and were probably thought of as entirely white. I don't much about know about how relations with Indians were handled.