Proudly American
Work backward from the first visible mark
Use a ground-level photo wide enough to include the cap, chase edge or nearby fitting if visible. Identify the highest place you can actually see discoloration, even if it vanishes behind a ledge. Note whether a neighboring face is clean. Color alone cannot identify a particular alloy, confirm a failed cover or distinguish metal runoff from another masonry stain.
Separate the repair from the clean-up
A contractor can inspect the metal edge, fasteners and roof interface while an appropriate masonry contractor evaluates the stain. Have them distinguish observed corrosion, a plausible runoff route and evidence still needed. A new stainless cover does not remove old staining from porous brick; a pressure wash does not stop runoff from a deteriorating fitting.
Set a finish expectation
The Brick Industry Association treats stain identification and cleaning as material-specific decisions. If appearance work is proposed, request a small professional trial and inspect it dry before committing to the whole elevation. Save dated photos of the trial and the upstream repair. A faint old shadow and a fresh expanding trail are very different reasons to call back.