pre-emancipation, it was black-on-white; post-emancipation, black-on-black was preferred.
In the pre-emancipation days, a "soul" signified a male serf.
1630s, "a setting free," from French émancipation, from Latin emancipationem (nominative emancipatio), noun of action from past participle stem of emancipare (see emancipate). Specifically with reference to U.S. slavery from 1785. In Britain, with reference to easing of restrictions on Catholics, etc.