Yeah, I wouldn't worry about the cause of it so much as how to fix.
To fix, just change the white point in Camera Imager:
More blue whitepoint in camera Imager = redder image
More red whitepoint in camera imager = bluer image
So, you can quite creatively mod the color to find the grey you are looking for.
Win 10 Pro 64, Xeon E5-2687W v2 (8x 3.40GHz), G.Skill 64 GB DDR3-2400, ASRock X79 Extreme 11
Mobo: 1 Titan X, 1 Titan Xp
External: 6 Titan X Pascal - 1600W EVGA T2
Plugs: 3DSMax, C4D, Daz, Houdini, Lightwave, Sketchup