If you right click on a Route or Track on the map, or within the GPX Explorer (GE), then you will on the context menu see Styles, and within that menu you can access the Route / Track Style. This will present you with a list of Styles you have available, and simply click on one to apply it to the selected Route / Track.
When applying a Style, you can either apply it to a Segment, which is the line connecting two Waypoints in a Route, or two Trackpoints in a Track. Alternatively, you can apply it to a complete Route or Track. In this way, you can colour a complete Route or Track, or opt to colour different parts different colours to suit your requirements.
The default Line Styles have been given descriptive names, but to understand them better, please open up the Line Style Manager from the Managers Menu on a PC, from Settings->Managers on mobiles and from the menu on macOS.
Once you have the Line Style Manager open, you can flick through the defined Styles and see their attributes. You can also within this screen edit the default Line Styles, or create your own.
When you next Sync your route files in GPX Manager (GM), your new Line Styles or alterations will also be synched and therefore be available on your other devices.
Tick Marks and Arrows
You can set the interval for tick marks and arrows within Settings->Styles / Icons