I really don't know the proper color of the green--but when we were in the muddy waters of the SFBay area (and we're back!) it became quite blackish and we'd use the brown scotchbrite "doodlebug" to scrub it off underwater to get back to greenish green
Hope that helps.
Regular bottom paint has the cuprous oxide (don't know if that's the right spelling and oxide...) rather than copper in it. That is why it doesn't last as long as the coppercoat which does have copper in it that slowly oxidizes. So--if the oxides are happening in the presence of the iron, it just turns out a little "different" I suppose.