Metal on the roof intermittently reflecting sunlight? (8)

I believe the answer is:

flashing

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'metal' is the definition.
Although both the answer and definition are adjectives, I cannot see how they can define each other.

I can't explain the rest of the clue.

Can you help me to learn more?

(Other definitions for flashing that I've seen before include "Waterproof strip" , "Shaped metal attached to a roof for strength and weatherproofing" , "Weather-proofing strip - like a strobe" .)

I've seen this clue in The Independent.

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