indigo vs violet

indigo and violet both are nouns.

Word	Noun	Adjective	Verb	Adverb
indigo	Yes	Yes	No	No
violet	Yes	Yes	No	No

As nouns, violet is a hypernym of indigo; that is, violet is a word with a broader meaning than indigo:

Other hypernyms of indigo include reddish blue.

indigo (noun)	violet (noun)
a blue-violet color	a variable color that lies beyond blue in the spectrum
deciduous subshrub of southeastern Asia having pinnate leaves and clusters of red or purple flowers; a source of indigo dye	any of numerous low-growing violas with small flowers
a blue dye obtained from plants or made synthetically

indigo (adjective)	violet (adjective)
having a color between blue and violet	of a color intermediate between red and blue