Finally settle after brief muddle in Navy (4)
I believe the answer is:
blue
'navy' is the definition.
(thesaurus)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for blue that I've seen before include "Dismal" , "Colour; squander" , "Varsity sportsman" , "Miserable - cerulean" , "Colour; depressed" .)