This reflects my experience in the East and West coasts. I haven't done much "heartland" travel.
I seldom see icons, and when I do, they are never green. The "stairs" icon is displayed (stick figure running down stairs), and that is in black-and-white.
The emergency exit "icon" is always a red "EXIT" against white, or a white "EXIT" against red. I'm pretty sure it's required by law.