This topic isn't my specialty, but I've been sorta looking into this myself.
Designing a HT room is a science by itself and there is esoteric ideas and products
that can rake up costs.
If projector w/unity gain screen;
I think you will need a darker room, ie black walls would be perfect. Realistically, any dark color is fine.
If projector w/high gain screen [Vutec Silver Star]
You can go lighter on the wall colors.
If projector w/black screen;
These screen a expensive and awesome in lighting conditions.
https://webspace.utexas.edu/phungjl2/Publication1.gif
If not projecting video;
Do what you want with color
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Sound conditioning
There are tons of products to place on the existing walls to sound condition, so
many ideas/products. You can to analyze costs on these products to see
what you can afford. I haven't looked at them yet.
In my case, whatever 'stuff' I place on the existing drywall, I will add curtains
to the walls to minimize higher frequency reflections sorta like what they do
in a real theater with fabric on the walls, but I might just place ordinary thicker
curtains that match the wall color just in case i want to move the curtains, maybe
place them on a roller?
Soo.. I have black sofas, recliners and I plan to paint my walls a burgundy color.
If you find something let me know, room decor isn't my thing...//content.invisioncic.com/y282845/emoticons/crap.gif.7f4dd41e3e9b23fbd170a1ee6f65cecc.gif//content.invisioncic.com/y282845/emoticons/crazy.gif.c13912c32de98515d3142759a824dae7.gif