Color lost on integration

I cannot solve a new problem, so I'm asking your help.   Here's the deal.

1.  Subs have color data, and if you calibrate the star colors on a sub, it works fine.  Here's a typical sub of Bode's Galaxy (a little amp glow in the upper right):  

2.  If I register, normalize, etc. and integrate with NO calibration frames, there is color data in the integration.  Of course, the picture isn't pretty due to lack of calibration frames.  

3.  if I register, normalize, etc. and integrate with calibration frames (dark and dark flat) the color data disappears and the integration takes on a green cast, I can't calibrate star colors because APP tells me color data is lacking, and it and looks like this:  

Nor does it matter whether I drizzle or not, or whether turn off "force Bayer CFA":  same green cast and lack of color data. 

4.  Now, here's what mystifies me.  I have taken obtained images with exactly the same scope, camera (ASI294MC Pro), light pollution filter, and calibration frames, and have had no problem whatsoever getting beautiful images out of APP.  For example, an image of the Trifid Nebula taken just two nights after Bodes Galaxy, and processed through APP, looks like this, and there was no problem with calibrating star colors:

5  And just a few nights before, I obtained an image of M101 with the same setup (different scope, however) that looked like this; again there was no problem calibrating star colors: 

Any idea what's going on?  

Thanks!