@jsmith I think you may have ended up in the right place on the internet. We have a very active and helpful community for (open source) photography and processing.
I think I have already provided you with a solution for the question you have. Copied from here:
Lightroom seems to have a very easy way to apply a color calibration based on a Color Checker chart. RawTherapee cannot do this easily. You would first need to create a *.DCP file (this contains the color calibration information), and apply it to all photo’s taken under the same lighting conditions. As I said, to create the DCP file is not easy and requires external tools. This is explained in more detail on the RawPedia page I link to.
If you have obtained a DCP file, you should open your photo, go to the Colour tab, choose “Custom” under Color Management and look up your DCP file.
@patdavid Not for RawTherapee indeed, but I think darktable has this functionality built-in since a few versions ago. Pretty nifty, we might borrow it at some point 