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Star colors will vary wildly with many factors besides light pollution. Altitude, transparency, natural skyglow. Blues are best shot at the zenith, red and green are not as affected at lower elevations. LP filters, Nebulae filters, etc... will have a red bias usually so what you end up with will always be different. There are some good tools in PI to retrieve the right colors, goodlook as also an excellent color balance algo. If you want to do a little pixel math in PI or CCD Stack the best way to get ball park is to select a part of the sky background without any stars (or very little) and no nebulosity. Look at the parameter called int mode then make a note of it for your red, green and blue channels. Take the highest value channel then calculate the difference to add/subtract to the other two channels and do a pixel math add/subtract to equalise the three channels. Then combine your color with the ratios 1:1:1. That will get you as close as it can be to the true color values.
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