21 C.F.R. § 73.50 – Ultramarine blue.

(a) Identity. The color additive ultramarine blue is a blue pigment obtained by calcining a mixture of kaolin, sulfur, sodium carbonate, and carbon at temperatures above 700 °C. Sodium sulfate and silica may also be incorporated in the mixture in order to vary the shade. The pigment is a complex sodium aluminum sulfo-silicate having the approximate formula Na7Ai6Si6O24 S3.
(b) Specifications. Ultramarine blue shall conform to the following specifications:
Lead (as Pb), not more than 10 parts per million. Arsenic (as As), not more than 1 part per million. Mercury (as Hg), not more than 1 part per million.
(c) Uses and restrictions. The color additive ultramarine blue may be safely used for coloring salt intended for animal feed subject to the restriction that the quantity of ultramarine blue does not exceed 0.5 percent by weight of the salt.
(d) Labeling requirements. The color additive shall be labeled in accordance with the requirements of § 70.25 of this chapter.
(e) Exemption from certification. Certification of this color additive is not necessary for the protection of the public health, and therefore batches thereof are exempt from the certification requirements of section 721(c) of the act.