You may have noticed the last few panels on that last page were strangely colored but not really figured out why!
In trying to represent a blurring of Diamonds' memory with the moment I tried to replicate horses' dichromatic vision, which probably looks a lot like protanopic/red-green color blind vision in humans. I imagine Diamonds, once a flesh-and-blood horse and a dichromat, remembers and dreams in two colors.