This is a long post, so I'm going to put the most important point first... I propose that if we want a system for standardized colors, that anyone photographing stones use a set of white, gray, and black cards for adjusting color balance. You can order cards from the links below, WilsonArt has free ones (shipping included) that are pretty close to commercial ones. The set on Amazon will be *very slightly* more accurate, but I don't think it will be that big of a difference for our purposes.
Now to the longwinded stuff:
The problem with getting accurate colors lies in the temperature, tint, and saturation of the photos... Most cameras will automatically adjust these things, but they are not 100% accurate. In fact, many cameras automatically increase color saturation because most photos will look better with a little more dramatic saturation and contrast. When marketing to consumers, most are looking for the camera that produces the best pictures, not necessarily the one that renders color most accurately.
All of these things can be adjusted later, if you can adjust to a known. When I've taken photos of stones in the past, if I wanted to represent them 100% accurate, I've actually held the stone up to my monitor and made adjustments to get it just right.
Now, even if I get a perfect representation of color on my monitor, it doesn't mean that you're seeing the same thing on your monitor... I am guessing that less than 0.5% of SRP users are viewing color calibrated monitors, which means that how colors render on my calibrated monitor probably don't look the same as they do on your monitor. The amount of sunlight, vs tungsten light, vs flourescent lighting in the room that you are viewing your monitor, and even the colors of the walls and carpeting will all have an impact on color rendition.
Sooo.... Now that I've written a dissertation on why we will never get 100% accurate colors of stones over the internet, here's my recommendation as to how to get them as close as possible:
1. We need to have standard (correct) white balance in the photographs. The standard white paper is on the right track... It would be best to photograph the stones with a standard white, a neutral gray, and a standard black card.
You can order a set on Amazon for $18.99: Amazon.com: Digital Grey Kard Premium White Balance Card / Gray Card for Digital Photography: Camera & Photo
OR... if you want free ones that will get you really really close, order the free sample chips from WilsonArt (get the matte ones)
https://samples.wilsonartcontract.co...e-d354-60.aspx
https://samples.wilsonartcontract.co...ea-d90-60.aspx
https://samples.wilsonartcontract.co...k-1595-60.aspx
2. If your camera can lock white balance from your white or gray card, do that. (consult your manual for instructions)
If the camera doesn't do custom white balance, then take a photo of the stone with your color cards in the photo. With a photo editing program that is capable of adjusting white balance (Photoshop if you have it) or the Gimp, which is free:
http://www.gimp.org/ adjust the white balance (set the white point, gray point, and black point with the cards).
3. Adjust the saturation of the image manually to get the final bit of accuracy.
(Again, this won't get the photos to 100% on everyone's monitor, but it will get them as close as we possibly can)
Finally... If that is too confusing for anyone: If you get a set of cards, and need help adjusting the white balance I'm more than happy to help out. Just send me a PM with the photo. It's a quick and easy adjustment to make if you take a picture of the stone and all three cards together. I won't be able to adjust the saturation without actually seeing the stone, but we can at least get pictures that are closer.