Indigo
A deep blue-violet hue lying between blue and violet, named after the indigo dye. It is also one of the seven colors Newton listed when he divided the rainbow.
That a rainbow has seven colors — 'ROYGBIV' — was Isaac Newton's choice. He first saw five in the prism's spectrum, but believing colors should number seven like a scale, he added orange and indigo. Indigo is the most disputed band today.
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