Drink up Earl Grey (4)
I believe the answer is:
pale
'grey' is the definition.
(thesaurus)
'drink up earl' is the wordplay.
'drink' becomes 'lap' (lapping is a kind of drinking**).
'up' says the letters should be written backwards (in down clue: letters go upwards).
'earl' becomes 'e'.
'lap' backwards is 'pal'.
'pal'+'e'='PALE'
(Other definitions for pale that I've seen before include "A bit of fencing" , "Without much colour" , "livid" , "wooden post" , "Having less colour than normal" .)