The question is a great one, but it does need a specific poem.  I think that there is much in Hughes' body of work that explores the pain of being black in America. There is not much else to say on it because being a person of color at the time of Hughes' writing did involve a great deal of pain.  Yet, I think it's important to note that what differentiates Hughes from other writers is that this pain does not blight or dull a sense of resistance and almost collective solidarity to strive to make things better.  Unlike some of his colleagues in the pantheon of African America literature like Dunbar or Cullen, Hughes is very passionate about the idea that while there is pain in the Black experience in America, there is also a reservoir of collective strength from which drawing can help make what is difficult something that represents a source of greatness, a source of inspiration for others.  For example, in the poem, "I, Too," there is pain at being humiliated, but a source of personal strength that sees one's contextual struggle in a larger scope and sequence.  In "The Negro Speaks of Rivers," one sees the wide historical presence Black people have held in world history, contributing to the understand that what is endured now is part of a larger dynamic.  In "Theme for English B," there is a certain amount of pain about what the speaker's existence is lacks connection to the teacher's or the colleagues', but there is a validation of voice present that acknowledges and accepts what is into being what should be.  In this light, Hughes' work does throw light on the pain of being black, but does so in a manner to ensure that this is not the only condition that being black contains.