Do you know the role of music in "Fences"?
Three kinds of music exist in the play: hymns, jazz, and a folk song. Rose and Gabriel rely on religious music for strength and inspiration. Rose does so more consciously because her life with Troy has been difficult; she sees the church as a refuge. Gabe tries to play music with his trumpet, but because it lacks a mouthpiece, he is unable to. Thus, he also sings, but primarily because he envisions himself as the Angel Gabriel.
Lyons is a jazz musician who seeks a career in music. When he invites his father to hear him play, Troy expresses his disdain for jazz when he declares he doesn't "like that Chinese music." Troy lives in the past when he was a outstanding baseball player; he makes no effort to appreciate "modern" music like jazz or, for that matter, Lyons' talent because this son is not an athlete.
Troy's song "Old Blue" is a song from the past that unites generations. He learned it from his father; by the end of the play Cory and Raynell are singing it together before they attend Troy's funeral. Not only does the folk song represent Troy's impoverished background, but it also shows Troy's need to have something or someone to depend on, even if it is only a dog. Notice that Blue "died like a man." Perhaps the song actually memorializes a real dog that Troy had. At any rate, the tone of the song is positive; he praises the dog more than he does either of his sons.