What do the different colors of highway signs signify Ex blue green brown?

The different colors of highway signs signify: 1.Ex blue:Used as background color for travel services information signs, emergency evaluation route sign. 2.green:Used as background color for the guides and information signs and for legend for the permissive regulation and the parking signs. 3.brown:Used as background color for the guides and information signs that are related to the points of recreational or cultural interest.