One of our favourite go to neutrals is Benjamin Moore Revere Pewter HC-172. It's grey without being too cold and because it's a mid tone colour it will fill your large space. A dark brown will certainly make the room cozier and more intimate (which may be what your contractor is trying to achieve) but you may not have as many options for accessories and artwork as you will with a lighter shade. Plus, repainting over such a dark colour can be challenge in the future.