Crossword Genius

Brown maybe, but there's one in Scarlet (5)

Ross

I believe the answer is:

study

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'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" .)

I've seen this clue in the Evening Standard.
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