There are lots of ways to determine RGB ratios but I don't think any is a magic bullet.
Some of the ones I have tried include:
- eXcalibrator
- using a G2V reference star
- using pre-calculated G2V ratios adjusted for extinction
- roughly lining up the R, G & B histogram peaks
- Unlinked stretch in PixInsight
- ColorCalibration in Pixinsight using a variety of white references (a galaxy, the star field, the whole image)
I didn't find that any of these did a good job in every situation. These days I use whatever gives me a result I like. Sometimes I blend a couple of different versions.
Cheers,
Rick.