In the night, arguably, it's black (3)
I believe the answer is:
tar
'black' is the definition.
(thesaurus)
'in the night arguably it's' is the wordplay.
'in' says the answer is hidden in the clue.
'TAR' can be found hidden inside 'night arguably ts'.
(Other definitions for tar that I've seen before include "Black viscid substance" , "Road-dressing for a sailor?" , "Familiar sailor - what a rat" , "Informal sailor or road-surfacing material" , "It may cover the road" .)