Positively rosy! (5)
I believe the answer is:
ruddy
'rosy' is the definition.
(thesaurus)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for ruddy that I've seen before include "Red in the face (like a duck?)" , "Dratted" , "Healthily red in face" , "blasted" , "Healthy reddish complexion" .)