saturated red vs. bright red
While it can be linked to the “hue saturation as emotional intensity indicator”, the dual shades of red we see within The Shining also have a direct reflection to the hurt and violence implied with the history references (see American History narrative), as well as the domestic violence narrative (see domestic violence narrative).
The red blood reflects the fresh attacks and wounds where the darker red reflects the violence that has permeated or ‘saturated’ the space.
It is no mistake that the elevator blood soaks over couches, and that Wendy watches from a hallway that is the same color red (while wearing 2 layers of Jack’s clothing)