Is Indigo really a colour of the rainbow?

Very good question asked on Colour Chat blog, and a partial answer, at the link below:

Also:

George Biernson, in 1972, wrote in the American Journal of Physics Why Did Newton See Indigo in the Spectrum? and “hypothesizes that Newton saw seven reasonably distinct colors in the artist’s paint mixture color circle (red, orange, yellow, green, blue, violet, and purple) and therefore assumed he could also see seven distinct colors in his crude spectral projections”.

Others have argued Newton was trying to add a seventh color to match the seven notes of the western world’s musical scale.

I will tackle the many problems of rainbow in my forthcoming series The rainbow is dead…long live the rainbow!!!

Stay tuned…

14 responses to “Is Indigo really a colour of the rainbow?

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  12. For Indigo, I do see a separate distinguishable color between blue and violet. The author is right about the mixture of the colors (wavelengths) can give the secondary colors. But in the eye each of the different types of cones, 3 of them though some says some women has 4 different cones, has a different response as one comes vary the wavelength. The cones down through blue wavelengths has definite peaks in the response to colors. The Red cone is of course centered in the “Red” wavelength, the Yellow in the “Yellow” wavelength and the Blue in the blue wavelength. To make orange that wavelength excites the red and yellow cones, green excites the yellow and blue cones. But violet excites the red and blue but not the green cone. The wavelength filters for the green prevents that. Now I don’t know the response of each type of cone to indigo light but It could have excite all 3 cones. There is good physical reasons about this as electrons are excited from a molecular valence band to the vacuum creating a free electron that can be used by the brain for the color.

    Now one can get purple from shining a blue and red light separately but one needs to adjust the relative intensity between them to get the violet one sees in the rainbow. That goes for all the other secondary colors.

    Because some people can see the indigo band and some may not be able to see it, that can be because of the difference in response between the cones people has. There isn’t any reason the filters between people need to be the same.

    So do we limit the colors definition to the lowest common denominator or the greatest?

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