Ah, you are correct. I had mixed up in my mind the Plessy v. Ferguson decision with the Dred Scott decision. Dred Scott is the one I was thinking of that led to the Civil War (you'll remember that one: it declared that slaves who went North were not freed but must be returned to their owners). Both were dreadful decisions on the part of the Supreme Court, and both were eventually realized to be mistakes. The Plessy v. Ferguson was the one that the Civil Rights act of 1964 eventually addressed. Sorry for the confusion.

(I adore Supreme Court history, but it's been years since I took AP American History.)