9 CFR § 316.5 - Branding ink; to be furnished by official establishments; approval by Program; color.
(a) The operator of each official establishment shall furnish all ink for marking products with the official marks at such establishment. Such ink must be made with harmless ingredients that are approved for the purpose by the Administrator. Samples of inks shall be submitted to the Program laboratory from time to time as may be deemed necessary by the inspector in charge.
(b) Only ink approved for the purpose shall be used to apply ink brands bearing official marks to carcasses of cattle, sheep, swine, or goats and fresh meat cuts derived therefrom. Any ink containing F.D. & C. Violet No. 1 shall not be considered an approved ink within the meaning of this paragraph.
(d) Except as provided in paragraphs (b) and (c) of this section, branding ink of any color, approved for the purpose by the Administrator in specific cases, may be used to apply ink brands, bearing official marks, to processed meat cuts derived from cattle, sheep, swine, or goats.
(f) Ink used must assure legibility and permanence of the markings and the color of ink shall provide acceptable contrast with the color of the product to which it is applied.