FD&C Blue 2 is the US regulatory name for the high-purity water-soluble dye known as Indigo Carmine. It produces a deep, royal to purplish-blue shade. Unlike the brilliant triarylmethane blues, it provides a more muted, classic indigo color. It is commonly used in applications like baked goods and confectionery. Its main limitation is its poor stability to heat and light, requiring careful formulation.
