Crystal clear without cover of powder (4)
I believe the answer is:
talc
'powder' is the definition.
(I know that talc is a more specific form of the action powder)
'crystal clear without cover' is the wordplay.
'cover' indicates the answer is hidden within the clue (I've seen 'covering' mean this).
'TALC' is hidden within 'crystal clear without'.
'of' acts as a link.
(Other definitions for talc that I've seen before include "Fragrant powder" , "In brief, popular body powder" , "Baby powder" , "(Mineral providing) powder" , "Bathroom powder (abbr)" .)