we had a dark purple carpet (looked like Welch's grape jelly!) this is what we did:
Painted the walls white then we splattered them. The colors we used were, red, green, yellow, orange, blue. (we used a couple of shades of blue and green)
At the time we did this, Scooby Do was what the kids liked, so we got a border with Scooby that had these colors in it. The room was sharp and we had many compliments on it. A lot of people thought it was wallpaper until they realized the pattern didn't repeat!
If you do this, be sure to protect your carpet well, put plastic over the windows, doors and protect all the trim. This way the room has a professional look to it. I have seen rooms splattered that the trim and doors were hit to, they looked "messy".
here's a link on the procedure if you choose to do this:
***I do not recommend the "balloon method", way to messy.