[OscarCunningham]

What I've heard as the explanation is that his "blue" referred to our "cyan" and his "indigo" referred to our "blue".

[aasasd]

Which almost exactly corresponds to the ‘rainbow colors’ as used in Russian (and probably other Cyrillic languages). The color swatches in the linked article are precisely Russian ‘blue’ for Newton's indigo and ‘lightblue’ for blue.