Sir Isaac Newton added Indigo to the rainbow so the seven colors would complement seven days a week, the "seven seas" and other mystical sevens. Indigo is a dark shade of blue. It is not its own color.
Indigo, as a color name, was around 400 years before Newton. Newton also supposedly added orange to the rainbow as well. That color name came from the fruit. It was originally called saffron. BTW, Newton could only see 5 colors.
Sir Isaac Newton added Indigo to the rainbow so the seven colors would complement seven days a week, the "seven seas" and other mystical sevens. Indigo is a dark shade of blue. It is not its own color.
Indigo, as a color name, was around 400 years before Newton. Newton also supposedly added orange to the rainbow as well. That color name came from the fruit. It was originally called saffron. BTW, Newton could only see 5 colors.