Like many other colors (orange, rose, and violet are the best-known), indigo gets its name from an object in the natural world - the plant named indigo once used for dyeing cloth (see also Indigo dye).

The color electric indigo is an approximation of spectrum indigo. This is the brightest color indigo that can be approximated on a computer screen - it is a color located between the web color blue and the color violet on the RGB color wheel.

The web color blue violet or deep indigo is a tone of indigo brighter than pigment indigo but not as bright as electric indigo.

On the old fashioned, now obsolete red-yellow-blue pigment color wheel (in which red, yellow, and blue were regarded as the primary colors and orange, green, and violet were regarded as the secondary colors), blue-violet was a tertiary color between blue and violet on the red-yellow-blue pigment color wheel. The other tertiary colors on a red-yellow-blue (RYB) color wheel were called red-violet, blue-green, yellow-green, yellow-orange, and red-orange.