Fight the sea (4)
I believe the answer is:
This clue could be a double definition.
'fight' is the first definition.
The definition and answer can be both human attributes as well as being singular nouns.
Maybe there's an association between them I don't understand?
'the sea' is the second definition.
Can you help me to learn more?
(Other definitions for blue that I've seen before include "Vulgar" , "This movie is X-rated" , "Oxbridge sports award" , "Unusual moon" , "Colour; depressed" .)