A ruddy Leftist! (3)
I believe the answer is:
red
This clue is a double definition.
'a ruddy' is the first definition.
(thesaurus)
'leftist' is the second definition.
(red is a kind of leftist)
(Other definitions for red that I've seen before include "Colour for danger" , "Colour of a cardinal's hat" , "- - poker: Kniphofia" , "River, its source in the US, flowing north to empty into L Winnipeg" , "Looking embarrassed" .)