Brown relish not good (3)
I believe the answer is:
tan
'brown' is the definition.
(tan is a kind of brown)
'relish not good' is the wordplay.
'relish' becomes 'tang' ('tang' can be a synonym of 'relish').
'not' suggests deleting specific letters.
'good' becomes 'g' (abbreviation).
'tang' with 'g' removed is 'TAN'.
(Other definitions for tan that I've seen before include "belt" , "Make black and blue" , "Skin colour after exposure to ultraviolet rays" , "Turn hide into leather" , "Catch the sun" .)