When does Nettie come into contact with American prejudice in Alice Walker's The Color Purple?

Nettie comes into contact with American prejudice when she takes the train to New York. In her letter to Celie, she explains the train had a restaurant and berths above the seats, but only white passengers could use the berths and the restaurant. Nettie, Samuel, Corinne, and the children had to content themselves with the "sit-down section of the train." The toilets were also segregated; Caucasians and African-Americans had to use separate ones.

Nettie writes that she encountered one other instance of American prejudice when she conversed with a white passenger from South Carolina. He asked her where she and her friends were headed, and Nettie answered they were going to Africa. The man found that information simultaneously humorous and offensive. He then made a denigrating comment to his wife about black people going to Africa.

Later, when Nettie met a representative from the Missionary Society of New York, she got the distinct impression from him that African-American missionaries like her could never be as successful in Africa as someone he knows: a fellow white missionary worker who "doesn't 'coddle' her charges" while she works with them.