The term blues may have come from “blue devils”, meaning melancholy and sadness
As time went on, the phrase lost the reference to devils, and “it came to mean a state of agitation or depression.”
The rock and metal culture have bound with the “sign of the red devil’s horn” and as the myth says, Satan loves metal!!
“Indigo” is the color of our skin, not exactly blue and not exactly red but somewhere in between…