What factor do Plessy v. Ferguson, brown v. Board of Education and regents of California v. Bake have in common

All three cases went to the Supreme Court for ruling.

All three cases involve policies that directly affected citizens of color in the United States.

Plessy v. Ferguson addresses the requirement that people of color sit in separate railway cars

Brown v. Board rejected segregated schools for children of color

California v. Bakke addressed the UC system's affirmative action policy, which benefits applicants of color.