A lot of the ambience around colleague comes from ham (7)
I believe the answer is:
amateur
'ham' is the definition.
(I've seen this before)
'a lot of the ambience around colleague' is the wordplay.
'a lot of' means to remove the last letter (most of the word but not all of it).
'the ambience' becomes 'aura' (I've seen this before).
'around' means one lot of letters goes inside another.
'colleague' becomes 'mate'.
'aura' with its last letter taken off is 'aur'.
'aur' enclosing 'mate' is 'AMATEUR'.
'comes from' is the link.
(Other definitions for amateur that I've seen before include "Person who does something as a pastime rather than a profession" , "Unpaid (sportsman}" , "he's not making any money" , "One who pursues an activity as a pastime only" , "enthusiast" .)