In older facilities, we see illumination for an exit sign coming from an external source. Section 1013.6 of the IBC regulates the graphics, illumination, and emergency power supply for such signs.
Although no particular color is specified for exit signs, it is REQUIRED that the color and design of the signs, the lettering, the arrows, and other symbols on the sign provide good contrast to increase legibility. The letters of the word EXIT MUST BE AT LEAST: