Neglected aftersun? Sunglasses can reveal it (6)
I believe the answer is:
unsung
'neglected' is the definition.
'aftersun? sunglasses can reveal it' is the wordplay.
'can reveal it' indicates a hidden word.
'UNSUNG' is hidden within 'aftersun sunglasses'.
(Other definitions for unsung that I've seen before include "evening prayer without a choir?" , "Remarked by no-one" , "Not properly acclaimed" , "Not honoured" , "Overlooked" .)