@royjohn the way around the monitor variability comes from photography. I’m also a photographer and have been color correcting my monitors for about 15 years. The second thing you need to get is a color checker card. Its simply a card with a bunch of precise colors on it including black and white. You can get a generic one or the datacolor passport (needs to be replaced every six months if it is heavily used) to color correct the images. Once you have color corrected the images and have color corrected your monitor the gemewizard will give you excellent and precise colors for your gemstones.
I already happen to have these two things. The monitor calibration tools run about 200-300 us dollars and the color checker can run from 50 to about 150 usd depending on where you buy it, how much tax is and how much shipping costs.
Unfortunately, I just upgraded to the Mac M1 chip and now my monitor calibration device is no longer compatible with my Mac and I have to wait for a new version to become available here. I also have a secondary problem that I am using a curved monitor and I am unsure about whether the monitor calibration tool will run on the new monitor. I have therefore kept my old MacBook pro for determining the color of my gemstones since it is compatible with my Datacolor Spyder 4Pro.
The last thing you will need if using software like the gemewizzard is something like adobe lightroom or photoshop in order to color correct your photos of the gem in question.
I have a setup I use to take photos of my gemstones. I have a Fuji Xt4 with the Fuji XF 60mm f/2.4 on a tripod. I built my own light box using posterboard and photography LED lights to light the gemstone from almost 360 in order to get the best lighting possible. The LED lights are 5000K light and mimic natural daylight so I can take the photos at any time of the day or night and get consistent lighting. (if you have a setup like this that you will just have to create the color profile once as long as you use the same lights, camera and lens).
You can go the analog way and use a color book. GIA used to have a gemstone color kit that had about 1000 color samples (little plastic strips) you could place next to your gemstone and then compare the color. That kit used to cost about 1000 USD but is not considerably more expensive since I doubt there are many complete sets available for sale.
I’m not sure what other tools there are out there. I think I ran across a book with for color grading a few months ago but that book also cost about 1000 USD and the paper will fade over time.
I did a quick search while writing this reply and found this analog book set you can purchase here.
Once again I do not have any relationship, financial or otherwise, with any of the items I have stated in this post.