Given that the Davis Cup recognizes only countries, not people,and since there are no countries named "black" (or, at least, none currently assigned to play the Davis Cup),the answer is: there have been no black winners of the Davis Cup.
UEFA Cup Winners' Cup was created in 1960.
Arab Cup Winners' Cup ended in 2002.
African Cup Winners' Cup was created in 1975.
Arab Cup Winners' Cup was created in 1989.
No they were never world cup winners.
African Handball Cup Winners' Cup was created in 1985.
European Futsal Cup Winners Cup was created in 2002.
North African Cup Winners Cup was created in 2008.
The Scottish Cup winners in 1902 were the Rangers.
The Dumbarton club were the SFA cup winners in 1882.
The Queen's Park were the SFA Cup winners in 1885.