On the way into work, I remembered that lenstip.com had tested CPLs:

http://www.lenstip.com/115.4-article...d_summary.html

But they actually state that the B+W MRC (ranked #6) that I use should be a little warmer, if anything. But blue does have a 5x greater "extinction coefficient" compared to red and green with the lower extinction coefficient being better.

JRW....that is one of the more extreme differences that I've seen using a CPL, but I can usually detect something. Plus, I like your idea of using a custom white balance. I'll try that, but was wondering if it changes as you adjust the CPL (rotate the dial)?

Thanks,
Brant