Myra Lightfoot was originally Myra Patterson who married Alexander Lightfoot. Both are in the 1870 and 1880 census records as Mulatto's.
It is hard to decipher if they were former black slaves or actual indians because census records don't define mulatto's at that time. I have read that some states defined anyone that wasn't white or of african decent as mullato, yet others defined mix-raced blacks as mulattos.
I have been researching this family line for a while and am stuck at the 1870 census which probably means that they were former slaves, since most were not counted on the 1860 census.