Outdoor tiles in dungeons?

I've seen in some dungeons of some quests, you can see outdoor features (like normal ground, not dungeon floor) in dungeons. A good example is Level 2 in Isle of the Winds. It's like the dungeon's palette is just a dark overworld palette. How do I accomplish this effect without making new tiles or palettes or editing existing ones? (And I mean on the PTUX tileset, mind you. I'm sure there's a palette there that looks like this, but I'm not entirely sure...)