I have also used a raw umber wash or a transparent black wash, which I learned from Bill Whitaker.
I like the cool gray tone for subjects lit with a cool north light (or equivalent). I prefer not to work on white canvas because it is too difficult for me to judge values against the white ground.
Although I generally use a wash made from OMS, for slicker surfaces(e.g., New Traditions L-600 which is REALLY smooth, or ABS plastic) I thin the paint with
www.studioproducts.com Underpainting medium. It dries very quickly and leaves a matte, slightly toothy surface so the first coat of paint I apply sticks more easily.