The initial iteration of Social Security excluded many types of temporary and informal labor. Although black workers were disproportionately impacted by these exclusions, the large majority (about 75%) of people who were excluded were white. One possible reason why these exclusions were in place is that getting accurate payroll figures for informal jobs is difficult. In any case, these exclusions were lifted between 1950 and 1955.
Keep in mind that Social Security was not the only New Deal program, and things like the Public Works Administration disproportionately benefited African Americans. The New Deal was extremely popular among African Americans, and is one of the major reasons why most African Americans switched over to voting for the Democratic Party. That's what makes the recent narrative that the New Deal was racist (and to blame for today's disparities) so strange.
1. https://newrepublic.com/article/155704/new-deal-wasnt-intrin...