if i recall, cato wore a black toga to stand out amongst the other senators, and probably to attract attention. he was a strict, unbribable traditionalist who sought to differentiate himself from his often corrupted contemporaries, and the black toga was one way he did this. i think he also refused to wear a shirt under his toga according the wisdom of the ancestors. if i am wrong, someone please correct me.
also, wasn't cicero older than potrayed in the show?