Closer to home, some people insist that indigo is a colour separate
from violet and blue. Myself, I simply can't see it as other than
bluish violet or violetish blue, yet I score as well as they on
colour-vision tests.
Newton made it up because, being a mysticist, he wanted there to be _seven_
colours in the rainbow.
However, Russian famously has a word for "light blue" (derived from "dove"),
a completely different one for "dark blue", and none for "blue"...
And there's a language somewhere in the Caucasus which has a separate native
name for "turquoise".