Cracked.com likes lists and recently put up a list for the 5 Most unintentionally offensive comic book characters ever.
DC comics' Legion of Superheroes' first black member (from '58 and '76, there had never been a black legion member), an African by the name of Troy Stewart from Marzal, a "nowyou see it, now you don't" island of the coast of Africa, made the list.
Tyroc made the list for a number of reasons: first, his awful powers - he yells out indecipherable words, which make cool things happen. Even the artist who conceived him admitted his costume was purposely made to look as ridiculous as possible. Third, a big part of why he was created was to explain the dearth of black representation in the Legion universe. Apparently, blacks were all Marcus Garvites living on the African island of Marzal or something.
Major Spoilers have a pretty cool breakdown and timeline of Tyroc in the DC universe.
However, one has seen the convenient ideas of self-segregation and mysterious islands-- this time a floating island "concealed in the mist off shore"-- used before to explain why there are no blacks in other comic book worlds. In 1973 Wonder Woman issue #204 a "floating island concealed in mist" was used to explain the dearth of dark skin folks among the many characters molded by the Greek gods. Apparently, , Nubia, the ruling queen of this "floating island," is Wonder Woman's twin sister separated at birth and raised by the god Mars to destroy the Amazons. Cover of issue #206:
Carol A Strickland and Insane Journal have compiled detailed breakdowns and timelines for Nubia.