Light, soft drink (4)
I believe the answer is:
pale
'light' is the definition.
(light in colour)
'soft drink' is the wordplay.
'soft' becomes 'p' (musical abbreviation for piano, 'soft').
'drink' becomes 'ale' (type of beer).
'p'+'ale'='PALE'
(Other definitions for pale that I've seen before include "stick" , "picket" , "Lightly coloured" , "Very light coloured" , "Dim - wan" .)