It didn't turn black. What happened is the yeast flocculated out. The yeast make it look lighter than it actually is. And then the volume of liquid makes it look darker than it actually is. 90% sure once you look at it in a glass or hydrometer tube it'll be close enough to the color you want.
Up Next: Best Bitter, English IPA, Spiced Winter Warmer, Brett. C. Old Ale
Primary: English Summer Ale, Coniston Bluebird Bitter Clone v1.5
Secondary: Sour Stout, Wild Bitter
Bottled: Sticke Altbier, Doppelsticke Altbier, Weizenbock, Berliner Weisse, Spruce Brown Ale, Arrogant Bastard Clone
Bottled for the long haul: Brett B. Tripel, Quadrupel, Tripel, Brett C. Oaked English Barleywine, Lamebic