One supplying air when tennis player gets colour back (9)
I believe the answer is:
serenader
'one supplying air' is the definition.
'tennis player gets colour back' is the wordplay.
'tennis player' becomes 'serena' (Serena Williams).
'gets' is a charade indicator (letters next to each other).
'colour' becomes 'red' (red is a kind of colour).
'back' shows that the letters should be reversed in order.
'red' in reverse letter order is 'der'.
'serena'+'der'='SERENADER'
'when' acts as a link.
(Other definitions for serenader that I've seen before include "Performer" , "a musical swain" , "Singer" , "Lovesick guitarist perhaps" .)