Colonist guzzling new prince's dairy product (9)
I believe the answer is:
emmenthal
'dairy product' is the definition.
(Emmenthal is an example)
'colonist guzzling new prince's' is the wordplay.
'colonist' becomes 'emmet' (type of ant - ants live in colonies).
'guzzling' indicates putting letters inside (I've seen this in other clues).
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'prince' becomes 'hal' (I've seen this before).
'emmet' placed around 'n' is 'emment'.
'emment'+'hal'='EMMENTHAL'
(Other definitions for emmenthal that I've seen before include "Swiss cheese with holes" , "Type of cheese" , "Swiss valley giving its name to a cheese" , "Something cheesy" , "Hard Swiss cheese" .)