I had a client request a blue background for a professional portrait.  Rather than purchase another roll of blue paper, I decided to try a different approach.  The set up was a neutral gray paper background.

Three lights.  A background light with a blue gel covering an Einstein 640 light/Pocketwizard PowerMC2, a main light (a second Einstein 640 shot through an umbrella) and a hair light (SB800/Pocketwizard FlexTT5) shot through a soft box.  These were all controlled with Pocketwizard MiniTT1/AC3 on the camera (D800).   This is a very easy set up and by simply changing the gel, I can get a different color.

The final result: a clean professional portrait.  Obviously, one can apply many different photoshop tricks to create some fun images.