How to render custom primitive color in XGEN using hair physical shader?

[Anonymous]

Dear forum members,

I've been experimenting with Arnold and VRAY hair shaders in XGEN for months. I can use ramp nodes and user data colors. The thing is that I use the hair physical shader (Maya 2018) with a custom color as a global expression in the primitive color attribute (with tube shade and color correction ON) and it's so perfect in the Viewport that I couldn't beat it with any other shaders.
Arnold can render the hair physical shader. My Arnold lights seems to be OK because I see the basic light brown color in the render view too. But I don't know how to add my color to the shader to get the same color as in the viewport. Changing the root and/or tip color results in a different color. Gamma correction failed. Switching to aiStandardHair and adding the same color as custom shader parameter failed. Creating Ptex map with the same color failed. Not resulting the same color.
I suspect that the primitive color is not overwriting the standard colors but somehow multiplies them. When you color preview the clumps in the modifiers tab a similar thing happens: Maya adds a random color TINT to the hair based on clump IDs in the preview. The other thing is that the hair physical has other components (1st, 2nd highlight, glint, transmission color). I revealed all the node connections in the Hypershade but I can't see anything how these are connected.
Please help me solve this problem.