Ahw, I think it was alien 4 were the photographer applied some specific treatment to the film. Well the symbolic part might be usefull, as well as the lights. Anyhow this kind of effects might be very important to convey the appropriate moods. Not only in the dreams, but also to give specific moods for differents locations and moments...
I think you overlooked sound effects. Correctly used they may help to give an atmosphere.
Also thank you for the dreamland hint, I will look for it. (Do you think there might be a french translation ?)

For Alien 4, it was all Carot and Jeunet, so the style was pretty much the same as in "La cité des Enfants perdus" (City of the lost children), and actually, that would be an excellent example of the kind of atmosphere you can create with the colors and costumes, etc ...
I was refering to the lights in the Alien 3, who are done by the same guy in Seven. You get this flickery, crappy film, dirty something style (check out a video of a band called Perfect Circle)

Mmmh, but does my examples help you anyway ? Do you se what I am talking about ?
I think it''s really about making a clear difference of graphic identity between RealLife, and Dream ... check out The Matrix, you jsut can''t miss it now that I told you.

youpla :-P