I decided that (a) the 'old' version of texturing and painting the 'plaster' on the walls was too dark and (b) it was too labour-intensive (paint everything sand, and then dry brush it, twice). So I've had a change of heart - I'm leaving it white, applying a sandy wash, and then a very light, white, dry-brush. The effect can be seen on the lower part of the wall sample above.