Every now and then, coloured part of puzzle (4)
I believe the answer is:
Here is my best explanation:
'part of puzzle' is the definition.
The answer and definition can be both related to communication as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'every now and then coloured' is the wordplay.
'every now and then' means one should take alternating letters (letters selected at regular intervals).
The alternate letters of 'coloured' are 'CLUE'.