red-purple vs reddish-purple

red-purple and reddish-purple both are adjectives.

Word	Noun	Adjective	Verb	Adverb
red-purple	No	Yes	No	No
reddish-purple	No	Yes	No	No

As adjectives, red-purple and reddish-purple are synonyms defined as:

red-purple (adjective)	reddish-purple (adjective)
of purple tinged with red	of purple tinged with red