The traditional approach is to generate a route and a track.
Assuming you start with a track, set it to display in dark green, which gives the best contrast against other map colours and is least likely to be confused with a road. Then use wingdb or similar to convert the track to one or more route segments as appropriate leaving the color as default pink or white as you prefer.
That way you get the static track shown as a narrow line highlighted by the wider route. It also means you get the turn by turn instructions from the 'follow road' route, and can clearly see if the Garmin is routing is attempting to take you away from the set track, though that becomes less likely as you set more route points/route segments. 50 route points per 200km is usually enough to keep you on on track, which is handy because thats the routepoint limit per route segment for (H)CX models.
Same approach works for Cx range though I don't think you can set colours, though that's a minor problem really
