Roof Discoloration Below Flue Exhaust

I can’t find much information about what is causing this white stain on the asphalt shingles below the HVAC flue exhaust on this roof. I’m curious about what the cause is and whether it is a defect that should be monitored or repaired.

Thanks

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That’s typical staining from the Flue material. Pretty common here in FL., and I never write it up. It’s only staining and does pose a threat of damage to the shingle.

Seen it before, not much to do about it. I see the next house has the same thing going on.

That is the zinc content bleeding out of the flashing and cleaning the algae on the shingles.

Is the rain cap painted white?

Bingo!

The rest of you are performing CNN Reporting…
Fake News

Most of the roof is stained.

The area below the vent is the real color of the roof.

Exactly