Operas with prominent characters of African heritage are many in history. But many were not initially sung by black artists.
Florence Cole Talbert-McCleave was the first African-American to sing the role of the Ethiopian princess Aida in 1924 in Italy. Gloria Davy (photo) was the first black American to play Aida at the Metropolitan Opera in 1958. Before that, the role was sung by non-blacks in dark makeup.
Another Verdi opera features a main character who's black. The Moor Otello is still being sung by some non-black performers in blackface. The Shakespeare original has seen black actors own the role. Ira Aldridge played Otello in productions during the 1820's. The most prolific Otello of our time is Placido Domingo, a Spaniard.
The English premiere of Koanga (1935) by Frederick Delius starred Australian caucasian John Brownlee and Russian diva Oda Slobodskaya in the principle roles. Now current productions always feature singers of African descent.
Enjoy this video of Leontyne Price who was perhaps the greatest Aida of the 20th century.