One of the earliest significant ads I can find in a mass market 
periodical offering nude photographs of African-American women.
(Or 
even women of color...)
From a 1956 issue of Frolic Magazine.  Scarce today, Frolic was printed 
on cheap pulp but the covers were bright and vibrant to stand out on the
 top shelf of shops.  In 1956 the magazine was published every two 
months with Luke Bailey as editor.  Harlem was about 100 blocks north of
 the editorial offices.
The photo sets offered here were common in the day, but to cater to a 
race market was not.  Mar-Mays photos MAY be yet another "branch" of the
 enormous "Marr" or "Marno" distributor of countless figure study 
digests documented as well as can be in the book 
PROTO-PORN: The Art Figure Study Scam of the 1950s.
The ad here ran four years after African-American photographer Cass Carr
 was arrested for organizing nude camera shots which used ethnic 
models...and Bettie Page.  Carr was a pioneer of sorts and lived in 
Harlem.  His studio was shut down by police as reported in Jet Magazine 
in 1952.  It is likely the photographs above came from informal (or even
 illegal) amateur camera club models such as those used by Carr.