Riding to hounds is flourishing (2,3,4)
I believe the answer is:
in the pink
If this is the answer I cannot explain how the clue works.
Can you help me to learn more?
(Other definitions for in the pink that I've seen before include "Enjoying perfect health" , "Thirteen [IN GOOD NICK]" , "suited for hunting?" , "location right here!" , "How Britain's colonies appeared on maps" .)