The color of exit signs is addressed in a September, 14, 1972 Letter of Interpretation in which OSHA says “any color, or color combinations, that is readily visible or distinctive in appearance on exit signs is acceptable to OSHA. It is possible that local building codes may require a certain color, but our standards do not.”
Also, 1910.35 allows for employers to comply with the exit route provisions of NFPA 101-2009, “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 ...”