Beginner with a non-beginner question

[The_Traveler]

Shoot with something like a color checker (Gretag Macbeth) in the field of view of the lens and illuminating light.
Learn to correct your file to the standard

Make certain that your monitor and the labs monitor are calibrated the same with a hardware color calibrator

 

[amolitor]

The magic phrase is "color management" and you need to make sure everything in the chain (camera, monitor, printer, etc) are all "color managed" and calibrated.

Unfortunately this includes whatever the guys at the lab are using to look at your pictures. Their monitor is going to be all over the place, likely. If you make a print, very very carefully, then they'll probably look at it under the wrong light, and it'll still be off.

What you CAN do though, it match your swatches, and THEN take a photograph of the swatches against the tooth, ideally under a couple different lights. Got a window? Shoot it with daylight. Then shoot it again under fluorescents, or whatever.

This gives the guys more information. It's really close to swatch D, but actually somewhere between D and E and, here's what it looks like.

It doesn't even matter if you're calibrated and color managed, the eye will adjust. Looking at their copies of the swatch, and looking at your pictures, they will be able to get a much better idea of exactly where the color should be.