Only the Ball Was White, inspired by Robert Peterson’s book published in 1970. This film was produced and directed by Ken Solarz in 1980. The film is a historical look at the Negro League, which existed because baseball was a segregated sport until 1947, when Branch Rickey brought Jackie Robinson to play for the Brooklyn Dodgers. The film basically covers the official formation of the Negro League in the early 1920s as well as an introduction to some of the more well-known players to rise up from the ranks of the Negro League including Satchel Paige, Josh Gibson and Roy Campanella.
For someone who knows nothing about the Negro Leagues, this film serves as a nice way to get an introduction to the subject. For more information about the Negro League, you should watch the made-for-cable Soul of the Game and the classic Bingo Long Traveling All-Stars & Motor Kings, you might be on your way to scratching the surface of Negro League Baseball.
If you want to read about the Negro League, the book Shades of Glory by Lawrence Hogan would be an excellent choice. This book was published by the National Geographic in association with the National Baseball Hall of Fame and Museum.