One more for the home!
Color belongs in the air, not just on the wall. Stained glass windows might seem way out of a student's price range, but they can be very affordable. Check antique stores, which regularly carry stained glass pieces, or look for a local stained glass artist. I have bought beautiful windows from Glenn Greene, a Pittsburgh, PA, artist. Local artists often will do custom pieces or even offer classes, so if you can't find what you want, ask. If you don't want a full window, go for a hanging 12" x 12" framed piece.
Then head to Ikea, and buy glass vases in coordinating colors. Put these on windowsills in rooms without stained glass windows, and you'll maintain the feeling throughout the apartment. This vase comes in several different colors, and is only $0.99. For a more artistic shape, go for this mouthblown vase ($4.99). Flowers optional.