How to set a default icon on overlays?
The GPX file format has no way to set an icon for a GPX waypoint, so Maps Pro will display a default grey marker on the map instead.

Maps Pro allows you to choose a default icon which will replace the default grey icon.
To set a default icon, go to Menu > Overlays > Add GPX/KML/... files > Pick your overlay in the list and the appbar will open at the bottom. Click options and click "Choose a default icon".

Windows will open a file browser where you can choose your image file (PNG / JPG / GIF / BMP accepted). Once you picked your file, Maps Pro will automatically reload the overlay, so you just need to press the back button to go back to the map.