With future stars Jerry Butler and Curtis Mayfield in the lineup, Chicago's Impressions boasted some of the strongest vocalists in ‘60s soul. But when Mayfield took over leadership after Butler's departure, they became one of the first black groups to speak out topically. 1964's “Keep On Pushing” and the following year's “People Get Ready” were two of the first civil-rights anthems, and remain two of the most stirring; Mayfield's message only got stronger with “Choice of Colors.” Leroy Hutson took over as lead singer after Mayfield's departure, and different lineups carried on until 1981.