Gluttonous man in a dull colour (6)
I believe the answer is:
greedy
'gluttonous' is the definition.
(similar in meaning)
'man in a dull colour' is the wordplay.
'man' becomes 'ed' (short for Edward).
'in' indicates putting letters inside.
'a dull colour' becomes 'grey' (I've seen this before).
'ed' put inside 'grey' is 'GREEDY'.
(Other definitions for greedy that I've seen before include "Gluttonous" , "Having excessive desire for food or money" , "Avaricious and acquisitive" , "Keen" , "Over-desirous of food" .)