If you are under exposing or over exposing, the color can change when you compensate for the exposure. Color casts can also change the color. If you are using natural light, clouds, time of day, building walls around you, green trees, etc., can all give color casts that our eyes adjust for and we don't notice.
Also it's possible your monitor is not showing colors correct in the blue spectrum. This could cause you to mis-correct them or think they don't look natural when they would on someone elses monitor. Having them printed is a good way to tell how they really appear.
The best and easiest way to make sure your color is correct, even if your monitor is not, is to use a neutral gray or white card in the picture somewhere. You can even use a Kodak or McBeth gray exposure card as long as it is a neutral gray. I perfer a white/gray/black card myself. That way when I bring my image into Photoshop I can open up the Levels palette, take the left eye droper and click on the black, take the right eye droper and click on white. Color balance is adjusted and true. Then when I adjust the exposure and contrast, I'm working with correct color and it gets adjusted evenly.
For jewerly, beads and other small things, the small WhiBal card or the small Calibration Target is idea. I like the WhiBal because it is really small and can be put in the image where it can be cropped out. They even have a key ring WhiBal card now.
Here is a link to the WhiBal:
http://www.rawworkflow.com/whibal/
Here is a link to the Digital Calibration Target:
http://www.photovisionvideo.com/stor...egory_Code=DCT
There are also other brands out there, McBeth makes one also. I have a McBeth Color Chart but they aren't cheap. Some people like the Expo Disk but I've never cared for it as it has it's limitations as well and is not cheap. For really cheap and can actually be very close, is a white coffee filter... unused of course or it throws the color off.
But to get accurate color without a lot of guess work, you really need a accurate color source to compare against.
Mike