What was “another big difference between Greenwood and Tempe?” a big difference was

From the text:

Another big difference between Greenwood and Tempe was the Negroes. There had been a few Negro porters on the train, but I was surprised by how many I saw around the Greenwood station. The freight workers on the platform were all Negroes, of course, but so were almost half the people around the station. The Negro women wore simple cotton farm dresses without hats; most of the Negro men and boys wore blue bib overalls, the same kind Grampa always wore.