In The Matrix, you could tell which "world" you're in by the general grade of color. When in the Matrix, everything had a greenish overtone, and when in the "real world" it was more blue. I really liked that use of color to be a part of the story telling process.
Steven Soderbergh's Traffic (2000) made heavy use of this, too, to distinguish different locales and parts of the story. The Mexico/Benicio Del Toro partions were heavy on gold/orange, burnt, sepia, while the Washington/Michael Douglas parts were blue, cool.
http://www.imdb.com/title/tt1119644/?ref_=nv_sr_1 - Fringe (2008)