Reds are turning out to be book lovers (7)
I believe the answer is:
readers
'to be book lovers' is the definition.
(I've seen this in another clue)
'reds are turning' is the wordplay.
'turning' indicates an anagram.
'reds'+'are'='redsare'
'redsare' anagrammed gives 'READERS'.
'out' acts as a link.
(Other definitions for readers that I've seen before include "Lectors" , "Bookish people" , "cheaters" , "Student textbooks" , "Book users" .)