In the meantime, I reloaded the files into PI and did the ColorCalibration step again.
This fixed a lot of the green color cast and made the pictures look much better than they were before.
I can see that there are big problems in the dim areas of the sky where the noise reduction dropped off too much data. Also, I had a heavy hand on histogram stretching, clipping many of the stars.
For what it's worth, here are the modified images.
|Crescent Nebula GSSP 2015 - Version 1|