periwinkle vs red periwinkle

periwinkle and red periwinkle both are nouns.

Word	Noun	Adjective	Verb	Adverb
periwinkle	Yes	No	No	No
red periwinkle	Yes	No	No	No

As nouns, periwinkle and red periwinkle are synonyms defined as:

periwinkle and red periwinkle: commonly cultivated Old World woody herb having large pinkish to red flowers

periwinkle (noun)	red periwinkle (noun)
edible marine gastropod	commonly cultivated Old World woody herb having large pinkish to red flowers
small edible marine snail; steamed in wine or baked
chiefly trailing poisonous plants with blue flowers
commonly cultivated Old World woody herb having large pinkish to red flowers