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For the construction industry, 1926.200(d) says, “Exit signs, when required, shall be lettered in legible RED letters, not less than 6 inches high, on a WHITE field and the principal stroke of the letters shall be at least three-fourths inch in width.”
However, for general industry, while OSHA regulations do not call for a particular exit sign color, 1910.37(b)(6) does call for exit signs to be “distinctive in color.”
OSHA’s 1910.35 allows for general industry employers to comply with the exit route provisions of NFPA 101-2000, Life Safety Code. According to this standard, “Externally illuminated signs shall ... have a [color] contrast ratio of not less than 0.5 ... Colors providing a good contrast are red or green letters on matte white background. Glossy background and glossy letter colors should be avoided ...”