What determines beer color?

Grain is by far the strongest coloring agent in beer. Beer color is measured on the Standard Reference Method (SRM) scale. SRM is calculated by passing light of a specific wavelength through a specific “thickness” of beer (one centimeter) and measuring the amount of light absorbed by the beer. Beers at 2-5 on the SRM scale are considered pale/gold and include styles like Pilsner and light lagers. Beer in the 7-15 range is considered amber, and styles include Oktoberfests, American Amber Ales and (paradoxically) English Pale Ales. At 16-25, we reach copper and brown, with styles like Bock and English Brown Ales. Above 25, we’re parsing shades of deep brown and black, topping out (in practical terms) at about 40, though the SRM scale theoretically runs well into the 70s and 80s in the most-roasted beers like Imperial Stout! Above 40, though, the beer is effectively black and opaque.