One of the things that I picked up in my travels of reading posts by Those-That-Know is: the Diffuse_color channel of the PoserSurface node has a heap of stuff going on behind it. Our first experiment is going to illustrate that point.

Let's create a high-resolution sphere from the Poser Primitives collection in Poser. To assign some materials to the top half and the bottom half of the sphere, click on the Grouping tool icon on the Editing Tool bar. This brings up the Grouping Editor dialogue.

What I did to make the top and bottom half of the sphere different materials, I first went into Camera Front View. On the upper left of the dialogue I selected "New Group" and called it "Top". With my mouse, I press down on the left-mouse button and drag diagonally over the top half of the sphere: a rectangle develops covering the visible area (i.e., the area facing you) you are selecting. When I let go, the top half of the sphere is highlighted in red. I click on "Assign Material" under Geometry Functions in that dialogue and type in the name of my new Material: calling it "Top Half". Voila, you've got a new material on the front of the top half of your sphere.

Do the same for the bottom half: I called the group "Bottom" and my material for that group "Bottom Half". I know: highly imaginative. We're going to go into the Material Room now, and select the Sphere Obect, and Top Half material. I've added a spots node and other stuff to the bottom for contrast.

Using the above maths concept, we're going to add Green and Red: 0, 1, 0 + 1, 0, 0 to get 1, 1, 0. We'll use the Color_Math node.

So, create a new Node:
New node >
Math >
color_math

Leave the default for Math_Argument, which simply means "what kind of maths this thingie actually does.
Change the colour of Value_1 to red... make sure it's 255, 0 , 0 in the Colour Picker.
Change the colour of Value_2 to green... make sure it's 0, 255, 0 in the Colour Picker.

Cool. A tool for adding Red to Green.  Our first node! WooHOO. Purpose as yet unknown, but that will eventually become clear. So we plug this into the Diffuse_Color channel of our PoserSurface. And let's render.

That's not yellow.
Read something about the Diffuse_color channel does a fair few things - like, heaps of stuff! Not sure what all it does, but it sure changes the colour a lot.

Also read that if you just want the nodes to control what you're doing, then disable the Diffuse_color channel and plug into the Alternate diffuse channel. Only your nodes will control things. That's what I'm led to believe!

Yep, that's yellow.

The biggest question is going to be: have I come to bogus conclusions about the Diffuse_color channel? is there something it does with the lights in the scene which makes the render come out less yellow?

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