Photoshop – image-processing by way of "hue-value-saturation" means to improve visual unity

I don't see any magic bullet fix for this, and it's probably going to be a subjective fix, 'by eye'

All I diid here is to use two color balance layers. One to reduce the yellow and the second the red.

Starting the layer masks filled with black to hide, I decided which page had a red or yellow hue. Dragged a selection around it, and filled the mask with white.

Then added a curves layer to brighten the darker areas also starting with a hide all mask.  

I selected each square in turn, and used a large, fully soft, 50% opacity brush to reveal the curve and brighten the background.   This was quick and dirty by way of example, and you would do better taking more time.

To take it a step further, I made a copy merged layer at the top of the stack.

Filled a new layer beneath it with and average of the BG colour (d5ab86)

And set the copy merged layer to lighten.  

That gave us a clean version of the lighter tones.

I made another copy of the Copy merged layer, and set it back to Normal. Then used Blend if to filter out the lighter tones leaving the blacks

It's all very subjective, and you could do much better working on one section at a time, but maybe it helped