Jeff Greene is the central character in A Solitary Blue; the story unfolds through his perspective. The novel opens with seven-year-old Jeff returning home from school to discover a note from his mother, stating that she has left and will not be back. In her message, she suggests that Jeff should learn to rely on himself and avoid disturbing his father. This sets the stage for Jeff's reluctance to openly express his grief or seek assistance.

Jeff is a timid, sensitive, and insecure child, constantly fearing that his father might abandon him if he becomes a burden. As Jeff grows older, he begins to take risks: he confronts his mother about her dishonesty and becomes more communicative with his father. Although his sensitivity makes him susceptible to emotional pain, his passion for nature and music helps him endure. By the novel's end, Jeff's hard-earned emotional growth reveals him to be a courageous young man, ready to embrace love and trust once more.

Jeff's father, known as the Professor, has been deeply wounded by his marriage to Melody. Despite his intelligence, he struggles with interpersonal communication and appears detached and indifferent. Jeff's perception of the Professor is shaped both by Melody's descriptions and the Professor's own reclusive nature. The Professor also experiences personal growth as he and Jeff learn to communicate with each other. Like Jeff, he has been hiding behind a protective barrier.

Melody, Jeff's mother, is perhaps the simplest character in the story, resembling Mrs. Jellaby from Charles Dickens's Bleak House. She is compassionate towards strangers but oddly neglectful of her own family's suffering. Her focus is on saving the world. Unlike the reserved Professor, Melody is outwardly affectionate, frequently hugging and kissing Jeff during his visits. Deprived of affection, Jeff mistakes this for love. Despite her deceit and manipulation, Melody isn't entirely bad. She seeks custody of Jeff only after learning that her grandmother, Gambo, has made him her heir. However, Melody doesn't want the money for herself; she intends to use it for her causes. When Jeff gives her Gambo's diamond engagement ring, she plans to sell it to fund a charitable mission to Colombia, South America. In her way, Melody aims to improve the world, but the pain and broken dreams she leaves in her personal life starkly contrast her noble intentions.

Among the secondary characters are Brother Thomas, Gambo, and Miss Opal. Brother Thomas is a colleague and friend of the Professor, also teaching at the university. He serves as a mediator between the Professor and Jeff, encouraging their communication and interaction. Gambo, Melody's grandmother and Jeff's great-grandmother, is wealthy and thrilled to meet Jeff, as he represents the last male of the Boudrault lineage. She shares the family's history with Jeff. Although Gambo and Jeff are not particularly close, she names him her heir, driven by pride rather than affection. Her distant demeanor sheds light on Melody's personality. Miss Opal, Gambo's maid, sacrifices her home to care for Gambo after she suffers a stroke. Jeff is astonished to discover she is older than Gambo. Following Gambo's passing, Jeff instructs the lawyer to transfer ownership of the house to Miss Opal, ensuring she has a permanent place to live.

The Tillerman family in Crisfield plays a crucial role in helping Jeff mend his emotional scars and regain trust in others. The family consists of Gram, an eccentric elderly woman who has taken in her four grandchildren; Dicey, the bright, tough, and honest eldest girl; James, the oldest boy, who is both intelligent and curious; Maybeth, who is gentle and warm; and Sammy, a natural fighter....