Perhaps surprisingly there are very few anthologies devoted to science fiction by African American writers -- primarily just this pair compiled by Sheree R. Thomas in the early 2000s. Thomas consciously evokes the astrophysical concept of dark matter as a metaphor for the widespread influence of "preeminent and emerging authors of the African diaspora," from W.E.B. Du Bois to Octavia E. Butler. The first book also includes essays by Samuel R. Delany, Walter Mosley, and Butler; the second, essays by Jewelle Gomez [the transcription of a conference panel], Nnedi Okorafor-Mbachu, and Carol Cooper.
(A more recent relavant anthology is AfroSF: Science Fiction by African Writers [isfdb], of original stories.)
Dark Matter: A Century of Speculative Fiction from the African Diaspora, (Warner Aspect, 2000)
[isfdb]
Dark Matter: Reading the Bones, (Warner Aspect, 2004)
[isfdb]