Pale Guardian covers bestseller with renewed energy (5)
I believe the answer is:
white
'pale' is the definition.
(pale in colour)
'guardian covers bestseller with renewed energy' is the wordplay.
I cannot quite see how this works, but
an anagram of 'with' is 'whit' which is within the answer.
'energy' could be 'e' (physics symbol as in E=mc2) and 'e' is located in the answer.
No letters remain.
This may be the basis of clue (or it may be nonsense).
(Other definitions for white that I've seen before include "Pallid" , "Drink that should be chilled" , "Colour of milk" , "Achromatic colour" , "wine" .)