I can see any dark colour best showing off jewelery better than whites, though it can/has been done in pure white in a few catalogs that I've looked at in the past. Darker colours just seem to give it a much richer/vibrant look.
different stones look better with different lighting...for instance i wouldn't use the same background for an emerald that i would a ruby...keep in mind complimentary colors!
Jols, keeping in mind that this is my VERY FIRST attempt at this and given more than 10 min to do this, I could do better, but for waht it's worth, here you go:
First attempt, little prep, obviously poor example.
The setup used for this and the next pic:
Last try before me needing to leave. It is better, but not what I would call ready. Given another 30 min and a few more test shots, I could do better... but at least this gives you a thought or 2?:
Ten minutes, 5 shots total. Newbie attempt but hey, I had fun!
I just tried out something that I think could be esily used with jewelery photography, to place a little emphasis on the item... its not jewelery, but try it out:
I was playing with selective colouring and instead of making one layer B&W, just motion blur it and bring out the unblurred layer on top. This could be an interesting effect to do with a special piece that you really wanted to make look different, IMHO.
I find the background distracting from the item. The left side of the ring's beautiful design fades a little becuase it reflects the colour of the granit counter top and it doesn't compliment the item.
I think one effect one could do is use a small stand, shallower DOF via bigger aperture and a greater space between the background to subject and a camera close to the subject for more background bokeh. I have to try something a little different for the next experiment.