I didn't see a post on this so i'm adding it. I had been hoping to find a digitized version of some of these and here they are.
This is a collection of a variety of cookbooks published over the years. It had been digitized by Michigan State University. There are 5 in particular by African Americans. I'll post them individually since I already did a link to "What Mrs. Fisher knows about old southern cooking" (1881) by Mrs. Abbey Fisher.

"The House Servant's Directory, or A Monitor for Private Families: Comprising Hints on the Arrangement and Performance of Servants' Work Boston:"
By Robert Roberts published in 1827.

Roberts was butler for Christopher Gore, Senator and Governor of Massachusetts.

View the book here
http://digital.lib.msu.edu/projects/cookbooks/html/books/book_05.cfm

It has recipes but is more a "how-to" manual for waitstaff, etc.