I'm curious about them, too - I see they're marked on the wiring diagrams, but I didn't see the wires for them anywhere by the window. Nothing is wired to the terminal on the switch in the back in mine - I'll have to look for the colors you mentioned.
I wired that fourth switch (I have a '95 30', so basically the same trailer) to turn on the marker lights. In mine, there is a connection for the marker lights under the closet, sitting on the wheel well - look for two green wires with a wire nut. I simply fished another green wire from the switch, behind the cabinets, to that junction and wired it in to that wire nut. Given the simplicity of this, part of me wonders if this is what Airstream might have been thinking - there was no other reason I could see to have that junction of marker light wire where it was, since it was only joining two wires, unless they just happened to hit the end of the spool in the most convenient location for me, or it was just a convenient point to connect two parts of the harness.
I recommend (but haven't done myself) a fuse and a diode so that the marker light circuit does not attempt to feed the rest of the trailer if you forget and leave that switch on.
I would love to find that valance light wire, though. I have some LEDs that I want to wire in that spot, so that 12 volt
feed would be great to have. I'm guessing it's behind the skin, but I'd love to be wrong about this. I hope someone with the valance lights can chime in about where the wiring is...