Erik,
I used G2V calibration quite seriously for a while (doing all the extinction calculations with a spreadsheet, etc.) and found it sometimes produced decent results. These days I often use eXcalibrator which is much quicker and easier so long as you can plate solve. It's worth checking out:
http://bf-astro.com/excalibrator/excalibrator.htm
I generally use a variety of methods to determine ratios for my colour combine and then pick the version I like the most. Most people appear to want pleasing rather than accurate colour
Cheers,
Rick.