The Collaborative International Dictionary of English v.0.48:

darky \dark"y\, n.
   a negro; an African-American; -- an older term now considered
   offensive. [Slang]

   Syn: darkie, darkey.
        [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

darky
    n 1: (ethnic slur) offensive term for Black people [syn:
         darky, darkie, darkey]