This requirement only applies when the law in question requires the government to have acted.
This state action requirement extends to a number of actions.
According to the Supreme Court in Edmonson v. Leesville Concrete Co., Inc., 500 U.S. 614 (1991), "Although the conduct of private parties lies beyond the Constitution's scope in most instances, governmental authority may dominate an activity to such an extent that its participants must be deemed to act with the authority of the government and, as a result, be subject to constitutional constraints."
D. The idea of separate but equal came about in plessy vs ferguson in the 1870s and brown vs board of education sought to discontinue the old practice of segregation in this instance in public schools.