The correct answer is: "Pessy's legal team claimed that the legal system in Luisiana inherently treat black citzens as inferior".
Plessy v. Ferguson is a case from 1896 which, back then, lead to the enactment of a landmark decision by the US Supreme Court .
Plessy's claimed were rejected. The decision issued by the Supreme Court allowed the proliferation of segregated public facilities under the belief that, if facilities were equal in quality, such system was not violating the Equal Protection Clause that guaranteed equality of rights for all US citizens. Such clause had been included in the 14th Amendment to the US Consitution, issued in 1868 during the Reconstruction Era.
Through this decision the US Supreme Court accepted the constitutionality of the denominated "separate but equal" lemma and, as a consquence, of segregation.