Shrimp exoskeletons contain a modified form of carotene (the molecule that makes carrots orange) called astaxanthin (the same molecule that gives salmon their color). In live shrimp, however, its pink color is not apparent because the molecule is wrapped in protein, giving a blackish hue. When shrimp (and lobster, for that matter) are boiled, the protein chains uncoil, liberating the astaxanthin molecule, and the shrimp turn pink.