This hue represents indigo, the elusive color that completed Isaac Newton’s seven-color spectrum in his 1660s prism experiments. Positioned between blue and violet at approximately 420-450 nanometers, Newton included indigo not for its visual clarity but as part of a broader philosophical belief in cosmic harmony, aligning the seven spectral colors with the seven notes of the musical scale. In the 1980s, early web standards introduced confusion when programmers without formal color theory backgrounds assigned the name “indigo” to a dark purple (#4B0082), a choice that diverged from Newton’s original. Today, we celebrate Newton’s Indigo at 435nm, the bright, electric blue-violet he actually observed. It’s a vivid spectral phenomenon that reflects his pursuit of divine mathematical harmony hidden within the physics of light.