Dizziness? I turn green first (7)

I believe the answer is:

vertigo

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'dizziness?' is the definition.
('vertigo' can be a synonym of 'dizziness')

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for vertigo that I've seen before include "Problem brought on by heights" , "that makes it hard to stand" , "Dizziness due to disorder in sense of balance" , "Dizziness at height" , "Feeling of dizziness generated by heights" .)

I've seen this clue in The Telegraph.

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