Slight colouring (5)
I believe the answer is:
tinge
'slight colouring' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for tinge that I've seen before include "A shade or a nuance" , "Slight tint" , "Colour slightly; trace" , "Touch (of colour?)" , "Slight but perceptible amount" .)