After Paul D exorcised the ghost from 124, why was Denver sad? What color is the pool of light in 124? Why is is there and why is it that color?

Chapter please?

The light in 124....

In the place where once a shaft of sad red light had bathed him, locking him where he stood, is nothing. A bleak and minus nothing. More like absence, but an absence he had to get through with the same determination he had when he trusted Sethe and stepped through the pulsing light.