@nprofile1q... @nprofile1q... The original Quake palette is easily available. But looking at it didn't help me gain any understanding how to create one myself.
The whole game being basically brown probably doesn't help, though.

I am now tending towards making a simple palette of 24 base shades for the overall aesthetics and making highlights and shadows on the fly, and then converting each texture to 32 indexed colors. Should at least achieve the graininess.