Color cast from Nik Silver, but only in some color spaces

[gjgoogl]

I have a color cast issue, in Affinity Photo 1.7.1.404, that I am trying to explain, in terms of the cause.  I use Nik Silver to generate B&W pixel layers.  Most of the time I am using RGB16, ProPhoto.  I was working on an image and noticed green and red in a layer that should be grayscale!

I have two computers, with dual monitors - all calibrated with Xrite.  I used the color picker to confirm that the RGB values are the same, so the areas are gray, but the display is not! The layer is the output from Nik SilverFX, without any toning applied.

I changed the pixel layer to grayscale, then the color bands disappeared.  I then tried various color spaces.  Strangely, the color cast that manifests in ProPhoto is removed if I switch  to sRGB:

I then gave ROMM a shot, but the color cast returns:

I then tried LAB16 and HDR32 - no color cast (I didn't upload the HDR32 example):

I am trying to understand what's going on, and how to explain the display output, at least to myself.  But, I can't since I don't really know what's at issue.

I also exported the file, about 572 MB, as a PSD, then opened it in PS CS6.  I don't see the color casts, banding of red and green in PS.

So, I am inclined to conclude that:

-it's not a hardware issue, as the banding shows up on two different computers (Nvidia or Intel graphics; Windows 10 Pro; four different monitors - all Xrite calibrated, recently) 

-is a software issue, probably related to Affinity Photo or Nik, since the color space does impact the display within AP.  ProPhoto and ROMM seem to have the same issues.

Output files (JPG, PNG, TIFF) do not show the color issues.

I generally Develop into ProPhoto 16-bit, to start, and only switch to sRGB and/or 8-bit on export.

I searched the forum content and could not find a similar color space issue.  Perhaps I don't know which terms will produce the similar issues?

Thanks for any suggestions,

Greg

[Chris B]

Hey gjgoogl,

I've installed a trial of Silver Efex Pro 2 and cannot reproduce this. Any chance you could attach an .afphoto file with the effect already applied?