I have yet to change my room's theme. Heh. We just moved in to this house in late July, and I didn't exactly get much of a choice between rooms.
My walls are a very light tan, peachy color, with a border at the top. [The border being dark blue outline, American Flags, ships, and a lighthouse. It looks all right.] My carpet is the same tan color, but much darker. I also threw in a few random colors around my room... A gray stereo, a bright yellow shelf-like hanger, a wooden desk, dark blue bed spread, and a Happy Bunny poster above my bed.
Pretty simple, I guess.