I think a black to white gradient or black to gray gradient is a perfect backdrop for beads with lots of color. I also really like the reflective backgrounds some people use like Sislonski (
http://www.etsy.com/shop/sislonski).
I have the following gradient backgrounds:
black to red
black to gray
black to white
cobalt to white
brown to cream
The only ones I use are the black to white or black to gray. By moving your piece around and adjusting the lighting you can use more of the dark or more of the light part of the background. Here's a couple examples: