Parse keys to return portion of key with Regex

Hi! Looking for some regex help again...

I have an analytics tool which allows me to take Regex and pull out specific parts of a key. In my example below, I'm looking to pull out the values which are in the third slot of the delimiter ":" and I can use the $ to reference a value to return.

Example Keys
     manifest_acquisition_summersale
     gglp:paidsearch_nb_b2b:thisisthekeyword:thisistheoccassion
     gglp:paidsearch_nb:paid keyword:rewardsclub
     gglp:paidsearch_nb:gifts:sale
     gglp:paidsearch_things:keyword_phrase

Expected Result
     (no match expected)
     thisisthekeyword
     paid keyword
     gifts
     keyword_phrase

What I've tried:
This failed -->

 ^gglp:([^:]+)$ 

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This failed -->

 ^gglp.*:([^:]+)$ 

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and then I referenced $1  to return what was matched

Results Returned with what I've tried:
None -- all tries have failed. :( Help please!