Is Indigo ACTUALLY part of a rainbow?

 The colors of the rainbow consist of red,yellow,orange,green,purple,blue and indigo. While some scientist do however believe indigo is not a color history begs to differ. So is indigo a color? or part of our mystical rainbow 

Isaac Newton launched the color indigo as one of the seven base colors of his work.  In the mid-1660s, Newton bought a match ups of prisms at a fair near the East India Company (Cambridge) which had importing indigo dye. 

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In his crucial experiment in the history of optics, Newton excelled in a narrow ray of sunlight through a prism to produce a rainbow-like band of colors on the wall.

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 He described this optical spectrum as a band had a continuum of colors. He named seven primary colours are Red, yellow, Green, Blew, & a violet purple; together with Orange, Indigo, & an indefinite diversity of transitional progression. He related the seven prismatic colors to the seven notes of a western major scale which he shown on a color wheel.

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As quoted he said  

I desired a friend to draw with a pencil lines cross the image, or pillar of colors, where every one of the seven aforenamed colors was most full and brisk, and also where he judged the truest confines of them to be, whilst I held the paper so, that the said image might fall within a certain compass marked on it. And this I did, partly because my own eyes are not very critical in distinguishing colors, partly because another, to whom I had not communicated my thoughts about this matter, could have nothing but his eyes to determine his fancy in making those marks   

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While some scientist do however believe Newton could have been mistake with colors that indigo was actually blue and the blue he seen was cyan. It is seen to be undefined.