If color-coded, which color is used to identify emergency, or supply, lines? Question If color-coded, which color is used to identify emergency, or supply, lines? Answers White Yellow Red Explanation Air lines are sometimes color-coded to help drivers avoid mistakes when coupling glad hands. Typically, blue is used for service lines and red is used for emergency lines. This questions appears in the following tests: Arizona Combination Kentucky Combination Louisiana Combination Maryland Combination Mississippi Combination Rhode Island Combination Rhode Island Combination Utah Combination Virginia Combination