I heard a Negro play (3)
The speaker has made a point of letting his audience know that the musician is African American. A few years after publishing "The Weary Blues," Hughes criticized a young poet for saying, "I want to be a poet – not a Negro poet" (Hughes, Langston. "The Negro Artist and the Racial Mountain." The Portable Harlem Renaissance Reader).
Down on Lenox Avenue the other night (4)
Lenox Avenue is sort of a code word with hidden meanings. The neighborhood around Lenox Avenue is prominently African American, but the jazz halls were a place where whites and blacks would come into contact socially.
With his ebony hands on each ivory key (9)
The ebony fingers coming into contact with the ivory piano keys shows the complex relationship between black and white people. Hughes seems to be saying that, yes, when the two groups come together the result is music, but the music isn't always sweet. This type of contact can make a bitter blues.