"Mitsuboshi Colors" is a slice-of-life manga series that revolves around the daily adventures of three young girls—Yui, Sacchan, and Kotoha—who form a group called the Colors. The trio dedicates themselves to protecting the peace and happiness of their hometown, Ueno, in Tokyo, though their missions are often lighthearted and imaginative rather than serious. Yui, the self-proclaimed leader, is energetic and confident, often coming up with elaborate plans. Sacchan, the most level-headed of the group, balances Yui's enthusiasm with her calm demeanor. Kotoha, the youngest, is quiet and observant, often providing unexpected insights or solutions to their playful dilemmas.

The narrative unfolds through episodic chapters, each depicting the girls' creative and often humorous attempts to solve problems or engage in activities they deem important. Their adventures range from searching for "treasures" in the park to devising strategies to outwit local shopkeepers or even confronting imaginary threats. Despite their grand ambitions, their efforts are frequently met with comedic mishaps or misunderstandings, highlighting the innocence and charm of childhood. The series also features recurring adult characters, such as Saitou, a police officer who humorously tolerates the girls' antics, and Daigorou, a local shopkeeper who often becomes the target of their schemes.

The manga captures the essence of childhood friendships and the boundless imagination of its young protagonists. It avoids heavy drama or complex plotlines, instead focusing on the simple joys and misadventures of everyday life. The interactions between the characters are warm and genuine, emphasizing their camaraderie and the playful dynamics of their group. Through its episodic structure, "Mitsuboshi Colors" offers a nostalgic and heartwarming portrayal of youth, creativity, and the small but meaningful moments that define childhood.