I'd go with whatever will be the least obtrusive. You've got a good amount of variation in the tones of the bs, and any grout that stands out could be distracting & busy. Get samples (my tile company gave me a color sample of the grout) and see what works best. Here's a photo of my finish samples. The stick-like, vertical piece in the middle is my grout:

light gray.

Thank you so much for your advice

I agree, pick one that blends with the tile, rather than define each tile by being very light or very dark. It will look less busy and more elegant.

Thank you. In this case would that be a very light grey or warm grey? Would white be to light?

I'd go white or as close to the cabinet color as possible for a contemporary/clean look. The darker you go the more you'll see the herringbone pattern. It's beautiful so far!

I would choose a light colour found in the tile. My taste would not be pure white, but a light gray, which will make the tiles blend rather than stand out individually. But it is a matter of taste.

to DIY2Much2Do - I saw your post of your newly installed Churchill soapstone countertops and wonder if you have a picture of the countertops oiled? If you get this message I would LOVE to see a photo. Thanks!

Grout can change a tiled backsplash very drastically. If you can, I would do up a sample board and try your top two or three choices. We have frosty carrina caesarstone in a bathroom and it seems to be a bit of a warmer white. I'd be worried about doing a real bright white grout and it not tying in well to the counter.