Final answer:
Homer Plessy was chosen by the committee to challenge the Separate Car Act because his light complexion would emphasize the arbitrary nature of racial segregation laws, leading to his arrest and the pivotal Plessy v. Ferguson case.
Step-by-step explanation:
The committee to test the Separate Car Act chose Homer Plessy because he appeared to be white due to his very light complexion. This fact was crucial to their strategy to argue against the law that mandated racial segregation in railway cars.
The Comité des Citoyens (Citizens' Committee) in New Orleans believed his racial ambiguity would highlight the injustice and irrationality of the segregation law, and further their argument that people should not be separated based on race.
Plessy's challenge to the law ultimately led to his arrest and provided the committee an opportunity to contest the law in court, resulting in the infamous Plessy v. Ferguson case.