Smear with colour, not quite right (4)
I believe the answer is:
blur
'smear' is the definition.
(I've seen this before)
'with colour not quite right' is the wordplay.
'with' means one lot of letters go next to another.
'colour' becomes 'blue' (blue is a kind of colour).
'not quite' means to remove the last letter.
'right' becomes 'r' (common abbreviation).
'blue' with its last letter removed is 'blu'.
'blu' next to 'r' is 'BLUR'.
(Other definitions for blur that I've seen before include "Obscure; smudge" , "Unfocused image" , "Indistinct mark" , "Mist" , "This Brit-pop band is a bit hazy" .)