Writer George dresses knight in blue (4)
I believe the answer is:
sand
'writer george' is the definition.
'sand' can be an answer for 'george' (I've seen this before). I'm unsure of the 'writer' bit.
'dresses knight in blue' is the wordplay.
'dresses knight' becomes 'n' (I am not sure about this - if you are sure you should believe this answer much more).
'in' is an insertion indicator.
'blue' becomes 'sad' ('sad' can be similar in meaning to 'blue').
'n' going into 'sad' is 'SAND'.
Can you help me to learn more?
(Other definitions for sand that I've seen before include "lover of Chopin" , "Dune constituent" , "George -, nineteenth century French novelist" , "Result of rock erosion" , "Grains by the sea" .)