Gigapixel for RGB Mattes - changing RGB color data

I’m using GPixel to resize 3D / CG renders that have both the full color image and a layer with RGB mattes where each item can be masked.

Passing the RGB layer through GP results in color shifts that do not maintain 100% R G or B. I can tweak these manually with levels, but its a bit unfortunate.

Anyone have tips? Is there any way to process both the full color and matte layer at the same time?
Thanks

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