Crossword Genius

Do such potatoes resemble tomatoes? (3)

Ross

I believe the answer is:

red

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'do' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.

I cannot understand how the rest of the clue works.

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(Other definitions for red that I've seen before include "- Cross; - admiral" , "Glowing" , "- - poker: Kniphofia" , "Colour of blood" , "Colour of 1 across" .)

I've seen this clue in the Evening Standard.
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