I would go with a soft neutral color or maybe a very light bluish color to complement the gray sofa.

picture would help

You've got good basics there. You can do a lot with it, but it depends on the feel and style you are looking for and how it fits with the rest of the house. For a more classic look, go for light grey-beige colour. I am not too found of the overall white look except for very modern open spaces. You can also go for very deep/dark vibrant colours as well: deep red/teal… any colour which you really like - but is has to be vibrant: gray coach over a dark brown wall is going to be sad... The more wall surface you have, the harder it become to use dark colours, but if you have shelving units or large painting, white/light accessories (lampshades, cushions) then it will work well.