Beginning to soar in the pink balloon (5)
I believe the answer is:
swell
'balloon' is the definition.
(I've seen this before)
'beginning to soar in the pink' is the wordplay.
'beginning to' says to take the initial letters.
'in the pink' becomes 'we'll' (I've seen this in another clue).
The initial letter of 'soar' is 's'.
's'+'well'='SWELL'
(Other definitions for swell that I've seen before include "Become larger like toff" , "Fop" , "Movement of the surface of the sea" , "Burgeon" , "succession of waves" .)