What follows is a rough attempt to follow your instructions, Bill. Still need to do the maths thoroughly... kinda did them, but wasn't sure if I was doing them correctly:

**def makeSurface():
  # Gamma-correction node
  gamma = Add(2.2).labelled("GammaCorrection")
 
  # Placeholder for colorMap
  colorMap = ImageMap().labelled("Color Map")
 
  # Colours to fiddle with
  ltBeige = Color(.98,.94,.88)
  ltBlue = Color(.91,.95,.95)
  
  # Underlying skin tone
  baseTone = SimpleColor(ltBlue * colorMap).labelled("BaseTone")
  
  # Complexion
  setSkin = Spots(
    Base_Color = baseTone,
    Spot_Color = ltBeige * baseTone,
    Spot_Size = .1,
    Softness = .35,
    Threshold = .7,
    Noise_Type = 2).labelled("Complexion")
 
    # Anti-gamma process: felt I had to take the baseTone value out once because it was added
    # into the setSkin twice
  linearColormap = ((colorMap + setSkin) - baseTone) ** gamma
 
  # Set up specular node
  setSpec = Blinn(1,.4,.4,.4)
  
  # Set up the Diffuse node, keep it from exceeding conservation of energy with Specular
  setDiff = Diffuse(linearColormap, .7 * (1 - setSpec))
 
 
  
  # Setting up PoserSurfacce
  s = Surface(1,0,0,0)
  s.Diffuse_Color = colorMap
  s.Specular_Color = WHITE
  
  # keeps diffuse_color from doing anything but just displaying in the pose room
  s.Diffuse_Value = Add(0,0)
  s.Highlight_Size = .02
  s.Bump = Sub(ImageMap(Background = Turbulence(.05,.05,.05,8,0,.5,.15)).labelled("Bump Map"),.5) * .03
  
  s.Alternate_Diffuse = (setDiff + setSpec) ** (1/gamma)
  
  return s
 
makeSurface()
**
Render reveals I'm using a really poor colorMap - seams everywhere!

two lights:
Infinite 1,256,1,1,1,65%, depthmap shadows...  :-P, no ambient occlusion
IBL 1,256,1,1,1,22%, no shadows, nothing else...
and I'll need to do a mask for the freckles and sheesh, all kinds of other stuff too. This is all very rough and I'll be playing much more with it, but I'm so excited about the fact that I've gained some confidence and understanding... mind you, still a huge way to go.

Is this shader valid? Probably not yet...

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] 

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