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Is indigo a blue or a purple?

Indigo is a color that falls somewhere between blue and purple on the color spectrum. It has a rich, deep hue that has long fascinated artists, designers, and scientists alike. But is indigo more properly classified as a shade of blue or as a distinct color unto itself? In this article, we’ll examine the history and science behind indigo to help shed some light on this age-old debate.

The History of Indigo

Indigo dye has been used for centuries to color fabrics, particularly in India and Asia. The dye originally came from the leaves of certain species of plants in the genus Indigofera, such as Indigofera tinctoria. Extracting indigo dye from these plants and using it to color fabrics has been dated back to Ancient Egypt.

In more modern times, Newton included indigo as one of the seven colors in his color spectrum, helping to cement it as worthy of being considered its own distinct hue rather than just a variant of blue or purple. The term “indigo” comes from the Greek word indicum, which means “from India,” reflecting the dye’s origins and prevalence in that part of the world.

Time Period Use of Indigo
Ancient Egypt Used as dye for fabrics
17th century Included by Newton in color spectrum
19th century Synthetic indigo dye developed

While natural indigo dye was historically important, the 19th century saw the development of synthetic indigo dye which could be produced on a much larger scale. This helped make indigo-colored clothing more affordable and widespread.

The Science of Indigo

From a scientific perspective, indigo is considered a non-spectral color. This means that indigo light does not correspond to a single wavelength on the visible light spectrum. Rather, indigo arises when our eyes perceive a mixture of wavelengths. Indigo sits at around 445-420 nm on the color spectrum, placing it between violet and blue.

When we look at the CIE chromaticity diagram that maps out all the colors our eyes can see, indigo occupies the portion of the diagram between blue and purple. On the diagram’s outer curved edge, indigo corresponds to approximately 270–295 THz frequency of radiation on the electromagnetic spectrum. So indigo can be thought of as a mixture of the blue (430–495 THz) and violet (668–789 THz) wavelengths.

Color Wavelength Range Frequency Range
Red 700–635 nm 428–480 THz
Orange 635–590 nm 480–510 THz
Yellow 590–560 nm 510–540 THz
Green 560–490 nm 540–610 THz
Blue 490–450 nm 610–670 THz
Violet 450–400 nm 670–790 THz
Indigo 445-420 nm 670-790 THz

So while indigo is closest to violet and blue, it exists in its own right as a mixture of those wavelengths. Our eyes perceive these combined wavelengths as the distinct bluish-purple hue of indigo.

Indigo in Art, Design, and Culture

The unique tone of indigo has long inspired artists and influenced culture. Here are some of the key ways indigo has made its mark:

  • Used in Renaissance era painting to create rich, vivid colors
  • Featured in the colors of national flags and emblems
  • Used as a symbolic color by musicians like Duke Ellington and Jimi Hendrix
  • Influenced fashion through indigo-dyed denim jeans
  • Inspired songs like “Mood Indigo” by Duke Ellington and Nina Simone
  • Revived by the textile industry through indigo-dyed carpets, tapestries, and clothing

Some examples of national flags that incorporate indigo include those from Nepal, the Cook Islands, and the Comoros. Indigo dyes and pigments continue to be widely used in textiles and fashion. The color brings a distinct, eye-catching quality.

Culture/Industry Use of Indigo
Art Renaissance era paintings
Music Symbolic color used by musicians
Fashion Denim jeans, carpets, tapestries
National identity Flags, emblems

Indigo’s prevalence across culture reflects its uniqueness as a color and shows how it occupies its own distinctive place on the color wheel.

Is Indigo More Blue or Purple?

When examining the technical definitions, cultural uses, and artistic applications of indigo, we can conclude that indigo is truly its own distinct color that cannot be classified solely as a shade of blue or purple.

While it shares similarities with both, indigo is scientifically a non-spectral color situated between blue and violet. And it has come to take on cultural and symbolic meanings independent of blue and purple. Indigo dyes have unique chemical compositions that produce the signature indigo hue.

Over time, indigo has come to be recognized as deserving its own distinct categorization as a tertiary color on the color wheel. When examining how our eyes perceive indigo wavelengths, how artists use indigo pigments, and the cultural associations indigo has taken on, it becomes clear indigo rightfully occupies its own unique place in the color spectrum.


So is indigo more accurately described as a blue or a purple? After digging into the history, science, and cultural applications of indigo, we can definitively conclude it is neither strictly blue nor purple, but deservedly its own distinct color.

Indigo sits between violet and blue on the visible spectrum, mixing their wavelengths to create a unique tone our eyes perceive as indigo. It has been used since Ancient Egypt as a dye with its own distinct chemical composition. Culturally, indigo holds meanings independent of blue and purple and appears prominently on its own in songs, fashion, and national emblem.

While indigo shares qualities with blue and purple, it has rightly earned its place as its own color. Over history, our eyes, artists, and cultures have recognized indigo as a distinct bluish-purple, neither fully blue nor fully purple. So in summary, rather than classifying it as one or the other, we can confidently say indigo is simply indigo.