Indigo, the Sixth Band

Indigo is the deep blue-violet that Isaac Newton inserted between blue and violet when he named the seven colours of the spectrum in the 1670s, and its presence there is more numerological than optical: Newton wanted seven colours to match the seven notes of the musical scale and the seven classical planets, and few observers can reliably distinguish a separate indigo band today.

As a dye, however, indigo is ancient and important, extracted from Indigofera and from woad, and it coloured everything from working clothes to the blue of denim; the trade in indigo shaped economies and, in the colonial period, systems of forced cultivation. In symbolic terms indigo carries the meanings of deep blue intensified toward the mystical, intuition, depth, the night sky. Its most prominent modern role is in the chakra system, where it is assigned to the brow or third-eye centre; that placement is a twentieth-century Western development and depends on Newton's seven-colour division rather than on any older Indian source.