Indigo is usually a color between blue and violet in the visible light portion of the electromagnetic spectrum. The wavelength of indigo is usually between 420 and 450nm, characterized by a dark gray blue purple color. Other things associated with indigo include:

• Indigo dye
• Indigo Bunting, a small North-American bird
• Indigo Girls, a folk-rock duo
• Indigo Internet, an ISP in Ireland
• Indigo, Victoria in Australia
• Indigo Books and Music, a bookstore chain in Canada
• Indigo children who possess distinctive psychic auras
• Indigo plant
• Indigo Application Server a Microsoft software product for building SOA systems with .Net technologies