The standard background color of U.S. interstate guide signs is green.
Green is the default guide-sign color used for directions, destinations, exits, distances, and other navigation information under the Manual on Uniform Traffic Control Devices. Interstate signs typically carry white lettering on a green rectangular panel, while the Interstate route shield embedded in the sign uses its own red, white, and blue design.
A common mix-up is confusing the route shield with the surrounding guide sign. The shield identifies the Interstate route; the green panel guides motorists toward places and road connections. Blue panels are generally reserved for motorist services such as fuel, food, lodging, hospitals, and rest areas.
Brown is associated with recreation, parks, cultural sites, and historic locations. White is commonly used for regulatory signs or certain boundary and informational signs, but it is not the standard background for ordinary Interstate directional guidance.