Hi @Stampede,
let me also add that if you can’t get your hands on a color target, you can still help yourself by creating a dual-illuminant DCP profile using dpreview’s “studio scene comparison” shots. They include a color target, and are taken using lighting that should emulate daylight and tungsten. They might not be 100% accurate, but from my (limited) tests they seem to do a decent job.
It’s unclear whether it is legal to generate DCPs from those shots and then distribute them with RawTherapee, but if you generate the DCP yourself and do not distribute it, I think everything should be perfectly ok.