Colleague goes around, starts to pose punny riddle (6)
I believe the answer is:
pepper
'riddle' is the definition.
(I've seen this before)
'colleague goes around starts to pose punny' is the wordplay.
'colleague' becomes 'peer'.
'goes around' is an insertion indicator.
'starts to' indicates taking the first letters.
The first letters of 'pose punny' is 'pp'.
'peer' going around 'pp' is 'PEPPER'.
(Other definitions for pepper that I've seen before include "Pungent seasoning and vegetable" , "Riddle" , "Spicy condiment" , "Condiment or vegetable" , "Pungent condiment" .)