Dont think there is much of a variation in B,G,B between object. But there is a slight variation depending on imaging altitude where Blue has a higher Atmospheric Extinction factor followed by green,
http://starizona.com/acb/ccd/advtheorycolor.aspx
I think the various weights of the filters is more to do with the characteristics of your optical path, ccd filters and Quantum Efficiency of the camera chip.
CCDstack has an automatic color calibration feature, I use G2V star calibration, but should try CCDstack to compare. I'm much a beginner in this area and would be interested to hear others replies as well.
Josh