29 CFR § 1910.144 - Safety color code for marking physical hazards.
(a) Color identification -
(1) Red. Red shall be the basic color for the identification of:
(i) Fire protection equipment and apparatus. [Reserved]
(ii) Danger. Safety cans or other portable containers of flammable liquids having a flash point at or below 80 °F, table containers of flammable liquids (open cup tester), excluding shipping containers, shall be painted red with some additional clearly visible identification either in the form of a yellow band around the can or the name of the contents conspicuously stenciled or painted on the can in yellow. Red lights shall be provided at barricades and at temporary obstructions. Danger signs shall be painted red.
(iii) Stop. Emergency stop bars on hazardous machines such as rubber mills, wire blocks, flat work ironers, etc., shall be red. Stop buttons or electrical switches which letters or other markings appear, used for emergency stopping of machinery shall be red.
(3) Yellow. Yellow shall be the basic color for designating caution and for marking physical hazards such as: Striking against, stumbling, falling, tripping, and “caught in between.”