Deep gray and all the other accents in silvery old wood and cream. This will add drama, allow the other elements to bring ion light and set off the concrete wall as a true feature. If you want light instead of drama, then go for a very pale beige stone. It will echo stone colours in both the concrete and rocks...

Beautiful clean modern kitchen! You have a great opportunity to put your personal stamp on the space with a unique backsplash. As you've heard already there are some different approaches. I'd probably place the backsplash up to the wall cabinets and up to the base of the hood. Then continue the backsplash at the same height (18"?) behind the sink. Then place an inspiring colorful picture above the sink to break up the wall. Here's a picture with pendants that aren't too obtrusive. Having multiple levels of lighting at different lumens makes a more inviting feel to the space. I couldn't decipher your flooring, but you may also want to consider adding some nature elements like a type of wood flooring, wood stools, etc. Good luck! If you need software to plan out materials check out our Home Designer software: http://www.homedesignersoftware.com/

I was about to say grey until I read the last line. What about a light brown carpet?

Is this picture taken during the day or at night? If it’s daytime your kitchen must not get much natural light. Go for white cabinets to reflect as much light as possible to brighten the room up. Boring but timeless & always looks fresh. For colour you could do a splash back, or just add colour via accessories such as a bright kettle/toaster set, tea towels etc., easier & cheaper to change if you get tired of it.