Turning white, section editor slipped away (7)
I believe the answer is:
elapsed
'slipped away' is the definition.
('elapse' can be a synonym of 'slip away')
'turning white section editor' is the wordplay.
'turning' is a reversal indicator.
'white' becomes 'pale' (I've seen this before).
'section' becomes 's' (legal abbreviation).
'editor' becomes 'ed'.
'pale' backwards is 'elap'.
'elap'+'s'+'ed'='ELAPSED'
(Other definitions for elapsed that I've seen before include "Pleased (anag.)" , "slipped away" , "Passed, of time" , "Went by" , "Pleased to have passed" .)