Two things effect how the background can be selected from the objects: the
actual color range you select and how it differs from the object, and
focus (boundary effect). Of course whatever color you choose is likely to
be cast into the objects so you want the background out of focus anyway.

I would choose blue. I am sure you will make some test images with
different light and backgrounds to be sure. Right? Ask this question in
the photoshop group for more info.

There seems to be a long tradition of using blue
backgrounds for exactly the purpose you describe,
and it's called bluescreening.

There are several chapters about bluescreen
techniques in "Photoshop Channel Chops" by
David Biedney, Bert Monroy and Nathan Moody.

The book may be out of print (my copy is
coyright 1998) but probably not too hard to find
used.

rafe b.
http://www.terrapinphoto.com

A couple of suggestions.  First try not to shoot the objects on the
background.  Elevate the objects well above the background (I assume you are
shooting down toward a table top here).  I do this by placing a sheet of
very clean glass on blocks placed at the corners.  How high you elevate the
glass depends on the objects you are shooting, the lens you are using and
the aperture selected.  I have found that for close-up work three to six
inches works pretty well.

Next use a background like a bright green (chromakey green for instance,
which is made for just this procedure).  Place your lights well to the side
and shoot across your objects.  That will give you good edges and separation
from the background.

With your objects well above the background and your lights at angles on the
sides the background should be very evenly illuminated and will be easy to
remove in Photoshop.  If necessary you can place a couple of small lights so
they hit the background without hitting the glass or jewelry to provide even
illumination.

If you shoot downward at an angle and the glass is clean it will disappear
completely.  You shouldn't need special non-reflective glass for this but if
you want just use an anti-glare 8x10 or 11x14 sheet of glass from a framing
shop.

HTH,
Sherman
http://www.dunnamphoto.com