Trots, imaginably (4)

I believe the answer is:

reds

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'trots' is the definition.
Although both the answer and definition are plural nouns, I can't understand how one could define the other.

I don't understand how the remainder of the clue works.

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(Other definitions for reds that I've seen before include "First snooker balls to be potted" , "Colours for communists" , "Colourful communists" , "Tidies up" , "These are not right" .)

I've seen this clue in the Evening Standard.

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