Also on a bright color calibrated screen here
I just looked at the overall image and the histogram.
I have seen very dark blue skies with the D810 at ISO 64 in bright daylight, and actually also from Leica M9 at low ISO, both without CPL right out of the camera raw files,,, I have not noticed any gray tones over that,,,
I have stopped using CPL due to problems with focus and loss of sharpness issues back in time when using the D3X with very sharp lenses, even stopped down.
I would recommend to try and shoot some more without the filter on the D810 and see if you don't like the colors better,,,
What raw converter?