Hi Heidi,
With sculptures, I wouldn't imagine you would be as concerned with color matching, but for others I wanted to mention a few things that will hopefully be helpful.
To match color precisely, the printer should be able to tell you what color space they are working in (i.e. RGB, sRGB, CMYK, etc.). Then you could provide them an image saved in that color space if you have Photoshop CS. If it's an odd color space, they should provide a downloadable color space profile for you to use. This is assuming that your monitor is calibrated, so that the image you see on your monitor in that particular color space will match the image on their calibrated monitor in that same color space. While it certainly would work to provide the printer a proof yourself, as Kim said, and have them match it, you're relying on them to adjust color correctly, and they're potentially messing up the balance of color/tone that you have in your image.
For those of us who don't have Photoshop CS, Photoshop Elements and many other image editing programs don't allow *real* conversions between different color spaces. They may allow you to save an image in different color spaces, but when they switch between different color spaces there will be a very noticeable (and unwanted) color shift in your image. There is a relatively cheap ($40) program called
Qimage that will convert without a change in color. It has a very different interface, and a moderately steep learning curve, however there is a 30-day free trial.
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