Koi-ai

A very dark blue. One theory says it has been used since the Muromachi period, but it apparently appears rarely in historical documents. Color names with "ai" (indigo) come in various depths, such as Fuka-ai-iro, Naka-ai-iro, Asa-ai-iro, and Shira-ai-iro. Perhaps Koi-ai means Fuka-ai-iro.