The Color of Water by James McBride is an autobiographical story told by a son and his mother. The chapters alternate, and each chapter is written in the voice either of Ruth or her son James. Your question has to do with devices of sound, which are something generally more concentrated and applicable to poetry than to prose writing. Onomatopoeia, assonance, consonance, rhyme, and alliteration are the most common devices of sound; and a poet will use them to add emphasis and meaning to the words he chooses.
In this case, it is perhaps the dialect the characters use which is the most poetic element in this story. Ruth, though she is white, speaks in the dialect of a black woman from the projects. She speaks directly and colorfully. James, too, speaks in a dialect, especially in his early years. Dialect is more about a rhythm than a sound, though, so it must be said that sound devices have very little to do with this piece of writing.