Indigo is a captivating color that falls somewhere between blue and purple on the color spectrum. Its exact hue has been debated for centuries, with different cultures and experts landing on different sides of the purple-blue divide. In this article, we’ll explore the science, history and meaning behind indigo to help settle the debate over whether this mystical color is more blue or more purple.
The Science of Indigo
Indigo resides next to violet at the end of the visible color spectrum. The wavelength of indigo light is about 445-420 nanometers. For reference, violet light has a shorter wavelength of about 380-450 nm, while blue wavelengths are around 450-495 nm. So indigo’s wavelength is right between blue and violet.
| Color | Wavelength (nm) |
|---|---|
| Violet | 380-450 |
| Indigo | 445-420 |
| Blue | 450-495 |
In terms of the physics of color, indigo light has a shorter wavelength and higher frequency than blue. So scientifically speaking, indigo is closer to violet than blue on the spectrum.
Indigo in History and Culture
The history of indigo as a color name traces back to ancient civilizations that produced the indigo dye. This dye was extracted from certain plants and was used to color fabrics a deep blue-purple hue. The word indigo ultimately derives from the Greek term for “Indian”, indicating the dye’s origins in India.
Sir Isaac Newton first labeled indigo as a distinct color in his color wheel in 1672. Newton placed indigo between blue and violet due to its intermediate wavelength. Other prominent color theorists like Moses Harris and Johann Wolfgang von Goethe also positioned indigo next to violet in their color studies.
| Color Wheel | Order of Colors |
|---|---|
| Newton (1672) | Red, orange, yellow, green, blue, indigo, violet |
| Harris (1776) | Red, orange, yellow, green, blue, indigo, purple |
| Goethe (1810) | Red-yellow, yellow-red, yellow, green-yellow, green, blue-green, blue, violet, red-blue, red |
Modern color theory has followed Newton’s classification of indigo as falling between violet and blue. This places indigo closer to purple than blue on color wheels and on the light spectrum.
Indigo Dye and Pigments
While indigo physically lies between blue and violet light, its appearance depends greatly on indigo dyes and pigments. The plant sources for indigo dye, like the Indigofera tinctoria plant, produce a distinct bluish-purple color when used for textile dyeing.
Early indigo dyeing spread from India through trade routes to Africa, the Middle East and Europe. The depth of color possible with indigo, and its resistance to fading, created a high demand for indigo-dyed textiles worldwide.
Synthetic indigo dyes were later created in the late 1800s. This allowed indigo dyeing to be done on a mass scale. Denim jeans owe their classic blue color to synthetic indigo dyes. So in many modern applications, indigo functions more as a blue dye.
Indigo’s Purple Hues
Despite its wide use for dyeing blue denim, indigo still retains some purple hues that allude to its place on the color wheel. Certain lighting conditions can bring out indigo’s subtle violet tones.
Optical mixing also comes into play. When placed next to red, indigo may take on a slight purple cast. This is due to the eye blending the two wavelengths and creating an intermediate purple tone.
The purple notes in indigo become more apparent when it is mixed with white. Adding white makes the color lighter and brings out its proximity to violet. A light purple indigo is used in web design, logos, and product packaging.
Is Indigo a Separate Color?
While Newton designated indigo as a distinct color, some modern color standards like RGB group it with basic blue. The RGB color model used for digital displays defines color using mixtures of red, green and blue light.
There is no unique indigo value in RGB. Full indigo hues are created by mixing blue with smaller amounts of red and green. Lighter indigo shades include more white.
| Color Mix | RGB Values |
|---|---|
| Blue + Red + Green | R: 75, G: 0, B: 130 |
| Blue + White | R: 114, G: 114, B: 196 |
Due to its approximation using primary colors in RGB, indigo is sometimes considered a variant of basic blue rather than its own distinct hue in digital formats. Yet the name indigo still persists culturally, even if it is technically a blue mix in digital media.
Conclusion
While it has associations with blue, particularly as a popular dye, indigo physically resides closer to violet on the visible spectrum. Historically, color theorists like Newton and Goethe also positioned indigo next to purple rather than blue based on its intermediate wavelength.
The exact hue of indigo continues to be nebulous, shifting between purple and blue depending on lighting, mixing, and cultural context. But its scientific place on the spectrum indicates that at its core, indigo contains more violet than pure blue, leading it to fall closer to purple in its essential character.
