RTF is a global modification that replaces all towns in the game.

and there's also a screenshot of the siege of a dark dwarf city, where there's a blue wall, but I didn't see it in the mod. Did they remove it, or is it still in development?

This is part of an additional mod for new territories; it's still under development because my computer lags due to the abundance of palm trees :D I want to release one version with dead, green vegetation and another with palm trees, but I haven't had the time yet.