GM Service Manual Online
For 1990-2009 cars only

When a route has been planned, it will be highlighted on the screen in blue. If you have set a waypoint(s) for your route, the colors on the screen will change. The highlighted route to the next waypoint or destination will be blue. All highlighted routes to further waypoints or destinations will be maroon.

Different colors are also used to distinguish between interstate freeways, state highways, county roads, major streets and secondary streets. Highways will be shown as a thicker line than a general street will.