Brown maybe, but there's one in Scarlet (5)
I believe the answer is:
study
'brown' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for study that I've seen before include "Den; closely look at" , "Room for work/reading" , "Contemplate" , "Revise" , "Scrutinize" .)