purple vs reddish blue

purple and reddish blue both are nouns.

Word	Noun	Adjective	Verb	Adverb
purple	Yes	Yes	Yes	No
reddish blue	Yes	No	No	No

As nouns, reddish blue is a hyponym of purple; that is, reddish blue is a word with a more specific, narrower meaning than purple:

Other hyponyms of purple include lavender, mauve, reddish purple, royal purple, violet.

purple (noun)	reddish blue (noun)
(Roman Catholic Church) official dress of a cardinal; so named after the Tyrial purple color of the robes	a variable color that lies beyond blue in the spectrum
a color between red and blue
(in ancient Rome) position of imperial status

purple (adjective)	reddish blue (adjective)
of a color intermediate between red and blue
belonging to or befitting a supreme ruler
excessively elaborate or showily expressed

purple (verb)	reddish blue (verb)
color purple
become purple