They dress in blue - not silver (7)

I believe the answer is:

coppers

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'they' is the definition.
Both the definition and answer are plural nouns.
Maybe there's a link between them I don't understand?

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for coppers that I've seen before include "Officers" , "The boys in blue (slang)" , "loose change?" , "Pence" , "Constabulary" .)

I've seen this clue in The Irish News.

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