I did a quick Google search but found nothing substantial. I assume such action was extremely taboo, but was it within the confines of the law?
Each state has their own slave code, but generally they defined slaves as blacks and mulattos and sometimes Native Americans. For example Virgia Slave Code of 1705 says "All servants imported and brought into the Country...who were not Christians in their native Country...shall be accounted and be slaves. All Negro, mulatto and Indian slaves within this dominion...shall be held to be real estate."