Sour milk - the colour of which has a greyish yellow tinge? (3-5)
I believe the answer is:
off-white
'colour of which has a greyish yellow tinge?' is the definition.
'off-white' can be an answer for 'colour' (off-white is a kind of colour). I am not certain of the rest of the definition.
'sour milk' is the wordplay.
'sour' becomes 'off' (synonyms).
'milk' becomes 'white' (I can't justify this - if you can you should believe this answer much more).
'off'+'white'='OFF-WHITE'
'the' acts as a link.
Can you help me to learn more?
(Other definitions for off-white that I've seen before include "Very slightly yellowish or grey" , "something like cream" , "Colour such as cream or bone" , "Slightly-tinted colour" , "Creamy?" .)