Like many musicians, Jimi Hendrix was self-taught. He could not read music.
As a composer Hendrix worked in colour. But his colour associations, as implied in “Bold As Love”, were not received but based on synesthesia. Blue is not sadness, it is “life-giving waters”; while Red is not anger but “confidence.”
That said, you would think Purple, for Hendrix, would be a mixture of “life-giving waters” and “confidence.” Maybe it is. Though for Hendrix, Purple is “anger." Both Neptune and Poseidon, being water gods, were capable of great storms.
Looking at Hendrix’s astrological chart I see that his Moon is in Cancer, a water sign, while in Chinese astrology, he is a Water Horse.