Pitcher John Ford Smith was the first Afro-American player to wear a New York Giants' uniform. He was a non-roster invitee with them in 1949 and 1950. This photo is from the New Castle (PA) News of March 15, 1949.
John Smith Register Statistics & History | Baseball-Reference.com
Photos of him may also be seen on the Negro Leagues thread at:
Sir Lurksalot photopack (Negro League and Nippon players) - Page 38 - OOTP Developments Forums
and
Sir Lurksalot photopack (Negro League and Nippon players) - Page 83 - OOTP Developments Forums