The colors of the rainbow are a natural phenomenon that has inspired wonder and symbolism across cultures for thousands of years. But did you know that the rainbow was not always thought to contain the same number of colors? Over time, changes in scientific understanding led to one color being removed from the common list of rainbow hues.
The Traditional Rainbow
For most of history, the rainbow was considered to contain seven distinct bands of color. The first known written list describing the rainbow’s colors appeared in the late 17th century. It contained the familiar sequence: red, orange, yellow, green, blue, indigo, and violet. This followed the long-standing folk tradition in many cultures of identifying seven primary colors in the rainbow.
This traditional order of rainbow colors had been inspired by the Greek philosopher Aristotle. In his treatise “On Colors,” written around 350 BCE, Aristotle attempted to link the rainbow’s hues to the seven planets, seven metals, and seven days of the week known in ancient astronomy. His color sequence put red first and violet last.
The Significance of Indigo
So why did the color indigo, which falls between blue and violet along the visible spectrum, gain such prominence in the rainbow? Some historians believe it was partly for mystical reasons. The number seven held spiritual symbolism in many early cultures, so having seven rainbow colors seemed fitting.
But indigo also filled an important scientific role. Isaac Newton identified the rainbow as the result of the refraction and dispersion of sunlight by raindrops when he published his discoveries in optics in 1704. His work revealed the visible color spectrum. Having seven colors, including indigo, allowed each to correspond to one of the seven notes in a musical scale. This supported Newton’s idea that nature followed mathematical patterns.
Indigo’s Questionable Status
However, later scientists began to question indigo’s place in the rainbow. In 1802, the English chemist William Hyde Wollaston determined that the human eye can distinguish only six distinct colors in the spectrum, not seven. He suggested removing indigo from the traditional rainbow sequence.
Other researchers noted that Isaac Newton had added indigo rather arbitrarily in order to match the seven musical notes. The narrow band of indigo visible along the spectrum could just as well be classified as blue or violet. As scientists’ understanding of light and color perception improved during the 1800s, indigo’s status grew more uncertain.
Modern Rainbow Colors
By the early 20th century, scientists and teachers had largely dropped indigo from lists of the major colors in the rainbow. Modern science recognizes the visible spectrum as a continuous distribution of wavelengths of light. But for simplicity, it continues to be divided into seven segments or color bands.
The current sequence is: red, orange, yellow, green, blue, violet. This reflects the true order of colors as dispersed by a prism or raindrops. Indigo is seldom included in updated rainbow color lists.
| Traditional Colors | Modern Colors |
|---|---|
| Red | Red |
| Orange | Orange |
| Yellow | Yellow |
| Green | Green |
| Blue | Blue |
| Indigo | |
| Violet | Violet |
Why Indigo Was Removed
So what led to indigo being relegated from the rainbow? A few key reasons help explain why this once-cherished hue is no longer considered a distinct rainbow color:
- Improved understanding of optics – Scientists like Newton gained a better grasp of how light splits into a spectrum.
- Advances in color perception – Research showed the eye detects only six main color zones, not seven.
- Arbitrary distinction – There was no natural boundary separating indigo from surrounding violet/blue wavelengths.
- Mathematical symmetry – Having six symmetric colors matched discoveries in visual perception.
Indigo was primarily included in early rainbow models for philosophical, mystical, and musical reasons. Once the physical properties of light were better comprehended, scientists realized indigo did not warrant its own separate place, but was just part of the blue/violet color continuum.
The Persisting Mystery of Indigo
The rainbow has held deep symbolic meaning throughout human history, so change has not come easily. The alluring color indigo still lingers in poetry, art, and popular culture. While no longer considered a distinct rainbow hue, it has not been entirely forgotten.
The musical group Indigo Girls, for instance, is a nod to the alluring mysticism ascribed to the seventh color. Movie director Richard Linklater titled his film Slacker “Indigo” in tribute to indigo’s uncertain status. And many artists continue to paint the rainbow with seven colors, unable to part with tradition.
So while modern science has technically relegated indigo to the rainbow’s past, its rich history keeps its memory alive. Indigo’s magic and intrigue remains woven through culture, even if its distinction as a spectral color has washed away.
Teaching the Rainbow’s Colors
The established list of rainbow colors also continues to heavily influence education. Many preschools and kindergartens teach young children the seven-color sequence using memory aids like “Roy G. Biv.” This helps familiarize kids with color names and order.
Yet it risks imparting outdated information given that contemporary science recognizes only six distinct rainbow colors. Some educational experts have pushed for schools to teach updated color sequences without indigo. But old learning tools persist out of habit and convenience.
Updating such early color instruction would better align with scientific accuracy. But the traditional seven colors are still deeply ingrained in songs, books, and other classroom staples. Indigo may have lost its luster among scientists, but it continues coloring children’s earliest rainbow perceptions.
The Rainbow’s Subjectivity
Beyond established color lists, viewing the rainbow also involves much subjective interpretation. No two observers will see the rainbow in exactly the same way. Its appearance depends on the angle of sunlight, position of raindrops, and the beholder’s individual vision and perceptual biases.
The rainbow spectrum is also continuous with no clear lines demarcating one color from the next. Where we draw boundaries between red, orange, yellow, and so forth is largely arbitrary – like seeing shapes in clouds. There are no “correct” rainbow colors, only conventions for simplifying its infinite variety.
So indigo’s past prominence and its modern ambiguity both underscore the rainbow’s inherent subjectivity. As our understanding changes, so do the meanings and categories we project onto this atmospheric wonder. The rainbow’s beauty is in its boundless diversity, not any fixed human labels.
Conclusion
The rainbow has long fascinated humanity across cultures and eras with its striking play of color in the sky. But one of those colors – indigo – has gradually faded from prominence in scientific understanding. Advances in optics, color theory, and physics led to it being dropped as a distinct rainbow hue alongside red, orange, yellow, green, blue, and violet.
Yet indigo’s rich symbolic history has kept its mystique alive in poetry, art, song, and popular teaching. Modern science sees indigo as merely part of the violet/blue color continuum rather than warranting its own separate designation. But this little-known history reminds us that nature does not always fit neatly into the categorical boxes we impose. The rainbow remains a phenomenon open to endless interpretation and awe.
