Spoil article that's in colour (5)
I believe the answer is:
taint
'spoil' is the definition.
(I know that taint is a more specific form of spoil)
'article that's in colour' is the wordplay.
'article' becomes 'a' (English indefinite article).
'that's in' is an insertion indicator.
'colour' becomes 'tint' (tint is a kind of colour).
'a' put inside 'tint' is 'TAINT'.
(Other definitions for taint that I've seen before include "contaminant" , "black mark" , "Adulterate" , "Rot, spoil, define" , "(Trace of) corruption" .)