Hi there, I would definitely go for glass & not tiles. Glass is much easier to keep clean! As for colours, if you have French grey units you could look at a slightly iridescent silver which would compliment well. Be careful with some colours if you are going to be a bit bolder as they will reflect & alter the appearance of the French grey on the cabinets. Get some samples & look at them in different areas under the units - the corners will look darker/lighter depending on natural light & if you have recessed lighting under the units.

I can't imagine tiles, the kitchen looks sleek, I'd be more inclined to do a glass splash back. Not sure on the colour though!

We're with Valduff. Shades of purple and plum can really add depth to a chic scheme like yours. Particularly with your gorgeous counter top. Grey is also a good call, as it will coordinate with your kitchen units but allow room to add coloured accessories. It can depend on the light quality in your room- we always recommend grabbing some tester opts in a range of shades. Paint your walls or A4 sheets, and see what the colours look like as the light changes throughout the day.

I think you should use white so the kitchen doesn't look choppy ,but if you still want color try this idea