West from Perpignan to get a taste of the Pyrenees

some start with A, some with C or D and others with N

French A roads are high-speed, limited access Autroutes, the equivalent of American Interstates or British Motorways. N roads are National Routes (Route Nationale); I believe they used to be the principal long-distance roads in France before Autoroutes were built. Many of them have now been changed to D (Departmental) roads, presumably because they've been transferred from national to departmental control. And C roads are generally very small, local roads.

You are correct in interpreting green to mean "especially scenic".

I have very limited experience traveling in that area--none of it driving--so this will probably not be very helpful:

• The route taken by the narrow-gauge SNCF Yellow Train is very scenic. Villefranche-de-Conflent is a very picturesque (but very touristy) fortified town. That end of the rail line is the prettiest. I caught glimpses of a road from time to time, so I think traveling roughly the same route by car would be possible.

• On the Spanish side of the border there are some very attractive stops outside the mountains. I don't know whether any of these places would be near enough to your route to be practical stops:

  La Seu de Urgell: very pretty historic area. There's a church or cathedral of some importance that I didn't have time to visit.

  Puigcerda (Poo cher dah): very colorful hill town, not small. The main town of the Cerdanya Valley. Has a helpful tourist office. Sits within 30-40 minutes' walk of the French border. This valley can be uncomfortably hot in the summer and should be quite pleasant in the fall.

  There are several small towns on the N-260 SW of Puigcerda that have that back-of-beyond feeling. I stopped off in Bolvir, Bellver de Cerdanya and Martinet. You're still in the valley--no terrain issues here. Limited food options in those places.

  NE of Puigcerda is the small Spanish town of Llivia, totally surrounded by France. Worth wandering around for a bit, and I saw multiple restaurants. I remember it as being larger than the three places to the SW.

None of the small towns I've mentioned is as colorful as Puigcerda or La Seu de Urgell.

I visited Foix, Peyrepteruse, Queribus and Alet les Bains in June. Foix was my favorite of the group. Nice castle with displays in most rooms. There are lots of other choices.

I don't recall setting my GPS to avoid main roads, but I was all over small 90 km roads (mostly D roads, rarely N) through the area. Some were spectacular roads cut from rock cliffs, many were along rivers or through forests, the entire area is gorgeous. I was expecting dry like Provence but it's very green and rolling hills (some bigger than others). The forests are thick and not the kind of trees that thrive without water. Reminded me of Burgundy.

The French I talked to said the Spanish side of the Pyrenees has more sun. I'm not sure if that means it's also arid?

Thanks to everyone for the info here! Very helpful for my trip planning.