Though they certainly didn't tell anyone:
In February 1861, just weeks after Louisiana seceded from the Union, Randall Lee Gibson enlisted as a private in a state army regiment. The son of a wealthy sugar planter and valedictorian of Yale's Class of 1853, Gibson had long supported secession. Conflict was inevitable, he believed, not because of states' rights or the propriety or necessity of slavery. Rather, a war would be fought over the inexorable gulf between whites and blacks, or what he called "the most enlightened race" and "the most degraded of all the races of men." Because Northern abolitionists were forcing the South to recognize "the political, civil, and social equality of all the races of men," Gibson wrote, the South was compelled to enjoy "independence out of the Union..."Gibson's siblings proudly traced their ancestry to a prosperous farmer in the South Carolina backcountry named Gideon Gibson. What they didn't know was that when he first arrived in the colony in the 1730s, he was a free man of color. At the time the legislature thought he had come there to plot a slave revolt. The governor demanded a personal audience with him and learned that he was a skilled tradesman, had a white wife and had owned land and slaves in Virginia and North Carolina. Declaring the Gibsons to be "not Negroes nor Slaves but Free people," the governor granted them hundreds of acres of land. The Gibsons soon married into their Welsh and Scots-Irish community along the frontier separating South Carolina's coastal plantations from Indian country. It did not matter if the Gibsons were black or white -- they were planters.The Gibsons were hardly alone in their journey from black to white. Hundreds of families of color had gained their freedom in the colonial era because they had English mothers, and within a generation or two, they could claim to be white. Their claims were supported by law, which never drew the color line at "one drop" of African ancestry in the antebellum era. Most Southern states followed a one-quarter or one-eighth rule: anyone with a black grandparent or great-grandparent was legally black, and those with more remote ancestry were legally white. Antebellum South Carolina, though, never had a legal definition of race. "It may be well and proper," a state judge and leading defender of slavery wrote in 1835, "that a man of worth, honesty, industry and respectability, should have the rank of a white man, while a vagabond of the same degree of blood should be confined to the inferior caste." Preserving the institution of slavery mattered far more than preserving the purity of white "blood." As long as people who claimed to be white were productive members of society -- in effect, supporting the prevailing order -- it made little sense to mandate a stricter measure of race.
I've spent much of my adult life studying various theories of race and racism, and the last few years in a rather intensive mode of study. In all of that time one inescapable conclusion has dogged me: Race is such bullshit.
It's important to keep that in mind.