You and I are singing off the same page, Rhionon.

Workflow for working those Stonemason shaders in Poser (and the mat room) was this:

set Diffuse_Color to white (if not already so)
Set Diffuse_Value to .8

... which of course brought up questions, because very often, the diffuse_color was like IColor(91,91,91) or a shade of grey with diffuse_value at 1. So, if you figure that grey is some percentage of white, and then I did a 91/255 * 100 = 35 (or .35) to give me a number diffuse_value might need to be... well, that didn't work right, for some reason. So, I'm lost, I just went and set color to white and value to .8, in the end. More than willing to be told off on this point by those-that-know - it seems we covered this somewhere in the distant past, but memory fails.

Then I plug the colourMap (ImageMap) into that diffuse_color channel. For all textures except those involving transmaps, I set filtering to None. No idea if that has any bearing on LuxRender or not. I know it's important to do for the Firefly renderer.
When I have a material the way I want it - and there's actually a few other things I do - I save the shader as an mt5 in a folder in my Materials library. That way, you'll see a picture of it to so you can use it later... which you will. Turns out there's only a dozen or so textures for like this whole scene. He's pretty clever, that Stonemason. Bump is left there, displacement is disconnected.

For desaturating a Poser colour, I'd be using the hsv node. However, testing in Lux has shown it isn't translated/recognised... only the fewest nodes are. I'm scrounging around to get some idea of how to build a shader in xml... going to start by finishing that LuxPose thread first.

Oh, up to 71 samples/pixel... and thank you for the kind words, Rhionon!

Monterey/Mint21.x/Win10 - Blender3.x - PP11.3(cm) - Musescore3.6.2

Wir sind gewohnt, daß die Menschen verhöhnen was sie nicht verstehen
[it is clear that humans have contempt for that which they do not understand] 

Metaphor of Chooks