While I was adjusting the shapes further on this, I kind of decided I would change the color theme for the surrounding panes. Since the center pane would be much realistic colors, I would make the others more monotonous as I quickly tried on the horse head here. I made everything reddish while keeping values.
It's quite interesting how human eyes compensate colors although they're NOT there.
I might change my mind later but I'll try this way, for now.