Line that's gold, but turns red (5)
I believe the answer is:
order
'line' is the definition.
(thesaurus)
'gold but turns red' is the wordplay.
I cannot really understand how this works, but
'gold' could be 'or' ('or' is the heraldic name for gold) and 'or' is found within the answer.
an anagram of 'red' is 'der' which is within the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
'that's' acts as a link.
Can you help me to learn more?
(Other definitions for order that I've seen before include "Command or request for goods" , "Tidy and settled condition" , "Right arrangement" , "demanding firm discipline" , "Command; neatness" .)