What is the author's style in Devil in a Blue Dress by Walter Mosley?

As a narrator, Easy tells his story in proper English. However, when he speaks to other blacks, his grammar becomes casual. For instance, Easy says in chapter two, "He got something to do with the fight?" The black characters, who have mostly all migrated from Texas, share Easy's laxity. For instance, Rosetta says, in chapter eighteen, "Why'ont you ast yo' friend anyway? He know where the whiskey grow."