What is the author's purpose in The Color of Water?
The author's purpose is to tell the story of his mother, who was born Jewish and married an African American man in New York, and to relate the courage it required for her to have an interracial marriage and interracial children. The book, written with chapters that alternate between the story of Ruth (McBride's mother) and the author's own story, is a testament to Ruth's fearlessness in both the black and white worlds at a time when that was almost impossible. McBride writes of his mother's "nonchalance in the face of what I perceived to be imminent danger from blacks and whites who disliked her for being a white person in a black world" (page 8). Ruth, her son writes, was indifferent to this hostility. She was, however, largely unwilling to discuss matters of race or identity with her children, who were left to piece together their identities on their own. Nonetheless, her children grew up with a sense of their mother's power and pride and a sense of the complex way in which identity is constructed in America.
Ostensibly, if you believe the subtitle, the purpose of the book is to pay tribute to his mother, Ruth McBride. The story is centered around the way that his mother worked tirelessly to raise a huge family in very difficult circumstances. The story also uses episodes where Ruth recounts her own life and her own family, making the story even more poignant and powerful.
I would suggest that his purpose is also to simply tell what is a very compelling story as most memoirs are set up to do. McBride emphasizes the importance and use of education in all of his family members' lives, so one could argue that it is another purpose.