I ordered this set of the color filters for my speedlight, and they arrived last night. They were only $9.99 on Amazon, and you can click on the picture for the product link.
I've started playing around with them this morning, and here's the first photos I took. I'm preceding them by a photo with a black background for comparison.
What do you think? Better with the color on the background?
The first colored photo was taken with a small softbox on the flash head. The second one was taken without the softbox. The flash angle was set to 105mm for both photos.
Here's what the setup looked like:
EDIT: Here's a couple more examples. This is fun!