What do the different colors mean on the route map in the Activity app on iPhone?

When I've completed a workout (run or bike) & am reviewing it in the Activity app in iPhone I can scroll to the bottom of the Activity page, tap the workout and see basic data. At the bottom of this page is a route map. The map is a multi-color track of my route. I'm trying to find out what the colors mean and haven't been able to yet. Thanks for your help!!