At first glance Greenland is an expanse of blinding white. But as my chopper swings low over the island, color catches my eye. For miles on end, bands of blue meltwater fringe the ice sheet. Fields of white are threaded with rivers, etched with crevasses, and blotched with lakes. There is also ice that appears neither white nor blue but rather brown and even black—darkened by a substance called cryoconite. This muddy-looking grit is a key topic of investigation for my four companions: photographer James Balog with his assistant, Adam LeWinter, and geophysicist Marco Tedesco with Ph.D. student Nick Steiner, both from the City College of New York.