The inclusion of indigo in the ROYGBIV spectrum of the rainbow is indeed a curious aspect of color theory that traces back to Sir Isaac Newton’s exploration of light and color. Newton, who first used a prism to decompose white light into its constituent colors, identified the colors of the rainbow as red, orange, yellow, green, blue, indigo, and violet. His decision to delineate seven distinct colors is typically attributed not just to observation but also to a culturally ingrained resonance with the number seven.
Newton's era was steeped in a context where numerology held spiritual and philosophical significance. The number seven, in particular, had longstanding associations with sacredness, featured prominently in various domains of life including religion, mythology, and the natural world. There are seven days in a week, seven traditional planets in astrology, and numerous mentions of the number in religious texts, making it a number often linked with completeness and divine perfection.
This penchant for the number seven is thought to have influenced Newton’s presentation of the spectrum. Contemporary science recognizes that the division between blue and indigo can be somewhat ambiguous, leading some to question whether indigo should be considered a distinct color within the visible spectrum or merely a variation of blue. The human eye perceives millions of colors, and the boundaries between individual colors can often be subjective and not entirely based on distinct wavelengths.
Moreover, modern interpretations of the rainbow no longer rigidly adhere to Newton's original seven-color division. Many educators and scientists now prefer simpler models, often combining indigo and blue into a single category, which simplifies communication and aligns more closely with the perceptual experiences of most people.
Despite this, the historical impact of Newton's decision remains evident in the persistence of the ROYGBIV acronym in many educational and popular contexts. Newton’s blend of empirical science and personal, perhaps even mystical, inclinations illustrates how the development of scientific thought can be deeply intertwined with the broader cultural and personal beliefs of its time. His decision to define seven colors of the rainbow provides fascinating insight into how science, philosophy, and spirituality can intersect.
