Different parchment color through Herbal section?

[npcompl33t]

Ok, wow @KoenG, you are on to something here. 

The current binding separates sheets on the same physical face that would have been together in singulion order. This means we can look for two effects: 

• Effects related to the current binding order should affect recto and verso roughly equally, and the other half's recto / verso should exhibit a difference that scales with the current binding separation.  
  
• Effects related to a previous singulion ordering should affect the sheet based on the physical face. We would expect probably Ar to be facing up, the two interior sheets to be the least exposed, and the Bv facing down, also less exposed than Ar.
  

It seems like Yellowing and Whiteness affect the pages differently. Forgive my hand created illustration. you can see 

• yellowing tends to agree with the binding order, Ar/Av are more yellow than Br/Bv. Recto and verso sides of A and B don't show more yellowness than the other. 
  
• However Lightness is not consistent with binding order, at least not for Herbal A. There could obviously be leather effects, but the asymmetry also looks like something closer to what we would expect from singulion ordering.