A warm tone (5)
I believe the answer is:
sepia
'a warm tone' is the definition.
(I've seen this in another clue)
'a warm tone' is the wordplay.
I cannot really understand how this works, but
'a' is found in the answer.
'tone' could be 'e' and 'e' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for sepia that I've seen before include "Old drawing" , "Brown of old photos" , "Reddish brown -- ie sap (anag)" , "Rich reddish-brown colour" , "Shade of brown, as in old photographs" .)