When we pull it apart piece by piece, we notice how our speaker pays careful attention to darkness and light throughout. He describes the "muddy" Mississippi turn "golden" as the sun sets and as night looms large. He talks of "dusky rivers" and of nights sleeping near the Congo River. In this way, our speaker highlights the conversation of race that takes place in the poem as well as the interplay of confinement and freedom that weaves in and out of the history he tells.