* Astronomy

The first recorded use of indigo as a colour name in English was in 1289.

It was Isaac Newton who first introduced indigo as a spectral colour. In the mid-1660s, when Newton bought a pair of prisms at a fair near Cambridge, the East India Company was beginning to import indigo dye into England, supplanting the homegrown source of blue dye woad. In one of the pivotal experiments in the history of optics, the young Newton shone a narrow beam of sunlight through a prism to produce a rainbow-like band of colours on the wall. In describing this optical spectrum he acknowledged that the spectrum had a continuum of colours, but specifically named seven colours: "The originall or primary colours are Red, yellow, Green, Blew, & a violet purple; together with Orang, Indico, & an indefinite varietie of intermediate gradations."
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[Hex Colour Code #2E0854]