I know this is not going anywhere (because Garmin has always had magenta for the route) - but can't we have a really strong single bright color for a route and the rest of the roads to be black/white? Say the route to be bright green and all other roads in black? It can be quite a struggle to tell the difference between the route's magenta and the other red colored roads around it.
When you're riding and have sunglasses the sunglasses reduce the screen's brightness and colors also so makes it so much harder to read the screen.