Highway exit signs (and most guide signs for directions and distances) are green with white lettering. When you’re driving on an interstate or major highway, the big signs that indicate upcoming exits, the exit numbers, the names of the destinations or streets off those exits, etc., are on a green background with white text.
For example:
An overhead sign might say “Exit 25 – Main St – 1 mile” in white on a green background.
The sign right at the exit might have a green background with an arrow and the exit number/name in white.
The signs showing the highway number and direction (like “I-80 West – San Francisco”) are also usually green with white text (though the Interstate shield itself on that sign is red/white/blue, but the sign background is green).
Green is the standard color for guide signs, which include exits, mile markers, city direction signs, etc. The reasoning: green signs give navigational information (while blue gives services, brown gives recreational info, etc.).
So the answer: Highway exit signs are green with white lettering.
