what describes the mood or feeling of the poem Harlem?

The speaker does not refer to a specific dream. Rather, he (or she) suggests that African Americans cannot dream or aspire to great things because of the environment of oppression that surrounds them. Even if they do dare to dream - their grand plans will fester for so long that they end up rotting or even exploding. The tone and mood is one of desperation, almost futility. As critic Arthur P. Davis writes, "When [Hughes] depicts the hopes, the aspirations, the frustrations, and the deep-seated discontent of the New York ghetto, he is expressing the feelings of Negroes in black ghettos throughout America." You can find more of this explanation at the GradeSaver  link below.