When the steamer leaves, Marlow describes the natives, especially the three men "plastered with bright red earth." What elements of the description convey how little Marlow understands about the natives' culture?

Marlow and white men in general are clueless to native customs. To these white Europeans, the Africans are merely savages. They fail to see the art or meaning behind their red paint, which Marlow dismisses as "red mud". Everything about these Africans remains alien to them and they, the white men, do not care to know.