Special permission had to be granted from the Hays Office in order to retain the famous miscegenation (interracial marriage) sequence in the movie. Miscegenation was banned as a film subject, and had been excluded from Show-Boat (1929).
Paul Robeson was the valedictorian of his graduating class at Rutger's College in 1919. He then earned a law degree from Columbia University in 1922 and was admitted to the New York bar, but he never practiced law. The acting bug bit him and led to an acting and singing career in the theater and films.
The design of the show boat is true to what a real show boat of that era might have looked like. This is partly because Jerome Kern and Oscar Hammerstein II wished it that way in their original stage instructions for the play, partly because of Edna Ferber's concern for historical accuracy, and partly because of director James Whale's sense of period design.