The Color of Water by James McBride is an interesting story in many ways, which should lend itself both to writing an essay and to creating an interesting, effective title for it. Consider the most unusual aspects of the story as potential for a title.
First, the story is told by two people, McBride and his mother. This gives two perspectives on everything that happens, so why not use that aspect of the story to be creative. Perhaps using the idea of "two" would be effective: two voices, two stories, two perspectives, two sides of the story, two narratives, two points of view, and more. Another word which might work to express the same idea is "pair," as in "A Pair of Perspectives." Even "dual" or "dueling" could be used if this aspect of the story is your focus.
Another aspect of the story is two distinctly different religions conflating in this autobiography. Jews and Baptists are distinctly different, yet both are significant in shaping both Ruth and James. So something about contrasting faiths or competing religions might work for you.
Though this is a lesser issue, the story takes place both in the South and in the North, which lends itself to more contrasts and comparisons.
The element of the story which offers you the most potential for both an essay and a title, however, is the secrecy and mystery which is created by Ruth and which prompts McBride to discover his mother's past. So words like "secrets," "mystery," "private," and "unknown" would help set the tone for an essay which focused on this aspect of the story. The entire story is a journey of discovery, so anything to do with following clues, seeking out truth, finding or discovering his roots, or learning the truth might be effective.
Really, the most important consideration when selecting a title for any kind of writing is to makes sure it applies directly to the content of your essay. If, for example, you are focusing on the religious aspects of the characters, the geographical references (North and South) would not be applicable. If, however, you were thinking about doing a character analysis of McBride, you could concentrate on the fact that he was suffering a kind of identity crisis which he eventually figured out was connected to his mother's mysterious past. In that case, something about him being a detective or being on a quest might be appropriate.
I would further suggest choosing a little bit of a twist to capture your readers' interest. Alliteration (as in "Pair of Perspectives") can help do that, as can a metaphor, such as McBride going on a journey, quest, adventure, or treasure hunt for his past or his heritage. Give your title a little mystery or play on words to attract your readers' attention. Whatever else you consider, however, the first thing must be that the title accurately depicts what is in your essay.