In court, earl turned red (6)
I believe the answer is:
claret
'red' is the definition.
(claret is a kind of red)
'in court earl turned' is the wordplay.
'in' is an insertion indicator.
'court' becomes 'ct'.
'turned' is an anagram indicator.
'earl' anagrammed gives 'lare'.
'ct' going around 'lare' is 'CLARET'.
(Other definitions for claret that I've seen before include "vessel might contain this?" , "Deep purplish-red" , "in one's veins?" , "Red wine from southern France" , "Irish county almost makes a red wine" .)