Dark purple. Seriously. Work your way up to umber and sienna colors.
What'll happen is that the reddening effect of the purple will make everything look like it is illuminated by a very dark and very red sunset. You can use your red-brown palette with it, and it'll make it look very red and very scary. What's worse, it'll remind people of something living and they won't be able to place their finger on it.
Friends of ours did a faux finish on the walls of their living room with a dark purple base. When it was all done, the room was really unsettling. "It's like being in a giant liver!" someone said. They repainted it shortly afterwards.