I think according to the law in Virginia at that time, they were considered slaves, no matter their color.
“Ellen Wayles Randolph Coolidge, Jefferson’s white granddaughter, who had moved with her mother, Martha Randolph, and her father and brothers and sisters to Monticello in 1809, knew the Hemings children well. All of Sally’s children were “fair,” she wrote privately to her husband in 1858, and “all set free at my grandfather’s death, or had been suffered to absent themselves permanently before he died.”
She wrote further in this revealing letter:
It was his principle (I know that of my own knowledge) to allow such of his slaves as were sufficiently white to pass for white men, to withdraw quietly from the plantation; it was called running away, but they were never reclaimed. I remember four instances of this, three young men and one girl, who walked away and staid away. Their whereabouts was perfectly known but they were left to themselves—for they were white enough to pass for white.
Ellen’s brother, Thomas Jefferson Randolph, in a confidential interview with an early Jefferson biographer, admitted that Sally Hemings “had children which resembled Mr. Jefferson so closely that it was plain that they had his blood in their veins.” In one case, he said, “the resemblance was so close, that at some distance in the dusk the slave, dressed in the same way, might have been mistaken for Mr. Jefferson.”
http://www.americanheritage.com/content/thomas-jefferson%E2%80%99s-unknown-grandchildren
Interesting. Thanks.