From “Minute Physics”. ( YouTube / Nebula )

Watch the full video: https://www.youtube.com/watch?v=9udYi7exojk

When Isaac Newton originally observed a rainbow of light split by a prism and made his labeling of the colors as "RedOrangeYellowGreenBlueIndigoViolet", the thing he called “blue” was indeed what we would now call blue-green, or teal or cyan – reminiscent of the color of the blue sky.
And what we now tend to call blue, Newton called violet – as in, roses are red, violets are blue. Dark blue.
He only included indigo in his fundamental "seven colors of the rainbow” so that they would match the number of notes of the western musical scale: Do re mi fa so la ti… yeah.

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Created by Henry Reich