What causes a beer's color?

A beer’s hue is largely a function of the malts used by brewers. Pale malts will deliver a straw- or golden-colored beer; deeply roasted malts, something resembling obsidian.

There are fine gradations, which brewers rank by SRM, or Standard Reference Measurement. A light pilsner, for instance, may hit the SRM scale at 2; IPAs are often in the 4 to 10 range; red ales, 30 to 40; while an imperial stout can top the chart at 100.