Writing at SCOTUSblog, George Mason University legal scholar David Bernstein has a superb essay explaining the importance of the Supreme Court's largely forgotten 1917 decision in Buchanan v. Warley:
Buchanan v. Warley is one of the most significant civil rights cases decided before the modern civil rights era. Starting in 1910, many cities in the South, border states, and lower Midwest, responded to a wave of African-American in-migration from rural areas by passing laws mandating residential segregation in housing. More cities were ready to follow suit if the laws survived constitutional challenges. Several southern state supreme courts upheld the laws against constitutional challenges. In 1917, however, the Buchanan Court unanimously invalidated a Louisville residential segregation law as a deprivation of liberty and property without due process of law.
Although some scholars have portrayed Buchanan as only vindicating white people's right to alienate property, the opinion's text belies that understanding. The right at issue, according to the Court, was "the civil right of a white man to dispose of his property if he saw fit to do so to a person of color and of a colored person to make such disposition to a white person." "Colored persons," Justice Day wrote for the Court, "are citizens of the United States and have the right to purchase property and enjoy and use the same without laws discriminating against them solely on account of color."