Turning blue, swimmer becomes ravenous (7)
I believe the answer is:
wolfish
'ravenous' is the definition.
(I know that ravenous can be written as wolfish)
'turning blue swimmer' is the wordplay.
'turning' says the letters should be written in reverse.
'blue' becomes 'low' (I've seen this in another clue).
'swimmer' becomes 'fish' (fish swim).
'low' reversed gives 'wol'.
'wol'+'fish'='WOLFISH'
'becomes' acts as a link.
(Other definitions for wolfish that I've seen before include "Ravenous" , "like Lupus?" .)