Homer Plessy, an octoroon or seven-eighths white, belonged to New Orleans's Committee of Citizens. Initiating a committee challenge to the state Separate Car Act (1890), Plessy bought an East Louisiana Railroad first-class ticket, boarded a “whites only” railcar, and was arrested. Suing the railroad for violating his constitutional rights, he lost in state court. His lawyer Albion Tourgée appealed to the US Supreme Court, which affirmed the state's ruling and the act.

Its Plessy decision debuted the “separate but equal” doctrine that legalized segregation. Accordingly, the Court approved a presumption of blacks’ inferiority that undermined their right to suffrage and allowed states to segregate public accommodations at will. Also consequential was the states’ power to define citizens by color. “There is no caste here,” Justice John Marshall Harlan wrote in dissent. “Our Constitution is color-blind, and neither knows nor tolerates classes among citizens.” Blacks hoped that Harlan's view would prevail someday.