The scale is one thing but it does not always correlate exactly with detail. I have two, single page, maps of the whole of France, both by Michelin and to same scale. One has all the detail stripped out, limiting itself to just the major roads and principal towns. The other isn’t so limited.
Green edged roads are those decided upon by Michelin as ‘scenic’. That of course does not always make them great motorcycling (or indeed, driving) roads, sometimes much above dawdling along.
Now that Germany has allowed Google to turn its street view on, you can get a very clear picture of what roads are actually like. Similarly, if the green lined road passes through village after village after village (all very scenic) when you really want to be pressing on along a perfectly good (but less ‘scenic’) road or two, then the map will tell you this.