Taylor doesn't need to shout at us about her message of racial injustice, because the events speak for themselves. Like Cassie's run-in with Lillian Jean Simms in Strawberry:
Behind him were his sons R.W. and Melvin. People from the store began to ring the Simmses. 'Ain't that the same little nigger was cuttin' up back there at Jim Lee's?" someone asked. (5.93)
'Yeah, she the one," answered Mr. Simms. 'You hear me talkin' to you, gal? You 'pologize to Miz Lillian Jean this minute.'" (5.94).
Pretty humiliating, right? You'd expect that there would be a general uproar in the Logan household after this, but no. Instead of heavy-handed editorializing, we get interaction between Big Ma and Cassie that gently reinforces the cruelty of this type of inequality:
"Big Ma gazed down at me, fear in her eyes, then back at the growing crowd. "She's jus' a child […] Go on, child … apologize." […] Her voice hardened. "Do like I say." (5.100)
Taylor quietly gives us troubling scenes of racially based brutality and discrimination, but she doesn't hammer home her point with extra commentary. The events and interactions speak for themselves.
And about that serious business: sure, Roll of Thunder, Hear My Cry has some light-hearted moments—but not many. Even at the Logan's festive Christmas dinner, the gift giving and jollity come with a heaping side of bleak: the tale of Mr. Morrison's family being slaughtered on a long-ago Christmas.