Green’s Dictionary of Slang

(US) a black person; thus Land of Sepias, Africa.

1929		W. Winchell On Broadway 29 July [synd. col.] Harlem cafes, where gorgeous looking white white girls unashmedly neck with dapper sepias.
1934		Dan Burley Plaindealer (Kansas City) 2 Nov. 6/1: Whte folks don’t forget altogether about the sepians in a heavyweight boxing match.
1935		Ted Yates This Is New York 3 May [synd. col.] Dorothy Sinclair may be the next sepia to ‘go Hollywood’.
1941		Pittsburgh Courier (PA) 8 Feb. 7/1: One of those bang-up jive letters [...] tells all about a sepia who knifed a fay.
1943		D. Burley N.Y. Amsterdam News 11 Dec. 6B: We’re padding in the north part of the Land of Sepias which is strictly a miz-riff cause the sways don’t savvy our spiel.