krausen can have dark particles pop up in the foam: it can be hop particles, proteins, and other residues. Completely normal.
On Tap: Barleywine, Coffee Oatmeal Imperial Stout (big big beer)
Fermenting: Double Simcoe IPA
On the Bench: Racer 5 IPA
"One of the first things early caveman did, when he crawled out of the mudd, was to make beer. And cavemen everywhere are still making beer...and drinking beer." - Jean Sheperd