Indigo is a deep and rich color close to the color wheel blue (a primary color in the RGB color space), as well as to some variants of ultramarine, based on the ancient dye of the same name. The word indigo comes from the Latin for "Indian", as the dye was originally exported to Europe from India.
It is traditionally regarded as a color in the visible spectrum, as well as one of the seven colors of the rainbow: the color between blue and violet; however, sources differ as to its actual position in the electromagnetic spectrum.
The first known recorded use of indigo as a color name in English was in 1289.