I was going to go look at Valve maps to give you advice, and I found out that Lumberyard and Gorge are the
only Valve maps to use an alpine setting. Maybe Doublecross too, but it's hard to notice because everything outside of the playing area is so dark. (By the way, Doublecross?
Another great example of how to visually differentiate symmetrical bases in TF2.)
In general, Red tends to prefer wood walls, slanted roofs made of corrugated metal, and a generally rough and ramshackle architecture while Blu uses mostly concrete walls and has an architectural style that's very clean and modern, dominated by right angles. Grazr mentions this when talking about
roofs in TF2, and while he follows that up by saying it's by no means a hard and fast rule, I feel it becomes more important if you have the layout of two bases facing each other. If the bases are identical in layout and there's not much space between them, you need to have them very visually distinctive, so that the player really feels like they're moving into a different part of the map as they advance. Grazr's own symmetrical map,
CP_Axle, is another example of a map that does this well.
(notice how the bases use different materials and are even shaped differently, despite having the same layout)
(um, if the image above doesn't show up, here's a direct link)
The problem with the "Gorge Style" is that it's basically just the regular Alpine Style plus industrial, white-dominated buildings, the latter of which leave little freedom for pulling off the kind of base detailing that a map like Arroyo needs. I doubt you're willing to completely overhaul the map's theme, but if you were, I think this map would look amazing with a theme that uses the alpine setting (so that you don't have to change the Skybox at all) and has bases that are kind of a cross between CP_Axle's architecture and Dr. Spud's Vineyard theme that he used in the
Artpass Contest (you'd have to get permission from the respective authors, of course). Or something like that. It would have to justify the trains, though. Hmm...
