Troy sings the song early in Act II, and then Cory and Raynell join in and echo it at the end. In this way, it is an individual and group song, and it is a primary source that, when shared, becomes a secondary one.
In Act II, Troy sings, "Blue was mighty true / Blue was a good old dog." And then, "Old Blue died and I dig his grave...Every night when I hear old Blue bark / I know Blue treed a possum in Noah's Ark." Cory and Raynell sing it too: "Go on Blue, you good dog you."
Blue is not only a dog, but it is "the blues," the Negro lyrical songs of mourning. The blues blend comedy and tragedy like no other art from. The lyrics look funny on paper (they're about a dog in heaven), but when sung, they elicit a catharsis.
The blues descended from slavery and old Negro spirituals, but then they took on a more secular identity in the 20th Century. They were a key to the past and a link to the future. Muddy Waters says "The Blues had a baby and named it Rock and Roll," so they are the basis for all modern American popular music.
Richard Wright says, “Blues, spirituals, and folk tales recounted from mouth to mouth . . . all these formed the channels through which the racial wisdom flowed.”
Ralph Ellison says, "The blues is an impulse to keep the painful details and episodes of a brutal experience alive in one's aching consciousness, to finger its jagged grain, and to transcend it, not by the consolation of philosophy but by squeezing from it a near-tragic, near-comic lyricism."
These songs are Troy's and Cory's and Raynell's way of responding to a world that has rejected them. Troy could be victim of tragedy (like a Greek tragic hero) and kill himself, or he could have a victory over his suffering and sing the blues. The song gives him a way of both coming to terms with and sharing his grief with others. By singing about Old Blue (suffering), Troy is keeping the dog (and his suffering) alive.