Erik-Sounds like the crosslinking is interfering with the pigment adsorption into the matrix. Two ideas-1)try a different pigment brand. Some pigment cariers will react with the dichromate and some will not. You can test this easily. Just mix a drop of dichromate solution directly with pure pigment concentrate from the tube. Let it dry. expose half of it and wash.
2) an absorption carier, like arrowroot starch, mixed with the CMC/pigment/ dicromate mix.
I could be off base here. It may be incompatability of the pigment or carrier with CMC. Then a different brand of pigment may help.
Bill