Very pale at sea, he washes it badly (2,5,2,1,5)
I believe the answer is:
as white as a sheet
'very pale' is the definition.
(I've seen this in another clue)
'at sea he washes it badly' is the wordplay.
'badly' indicates an anagram (letters in the wrong order).
'at'+'sea'+'he'+'washes'+'it'='atseahewashesit'
'atseahewashesit' is an anagram of 'AS WHITE AS A SHEET'.
(Other definitions for as white as a sheet that I've seen before include "Like a blank page" , "ghastly to look at?" .)