I'm not sure what they've used here, but I like to use snow white or antique white depending on the other colors in the kitchen. In a kitchen with more dark tones like this, antique white is probably a good idea. There's also Platinum if you're looking for a gray-white.

what's the size of the glass tile?

I agree with Rebekah on the platinum color. This is a very versatile color and will also change depending on what you put it with. It is a very soft gray, but different than the usual white. It goes well with greens, grays, black, blue, and white. Hope that helps.
Charmean Neithart

what colour is this tile?

This looks similar to our 'smoke' or 'surf' colors. We reccomend getting a few samples and putting them in your space. Glass tile tends to be reflective and take on the surrounding hues of a room so the same color will look different in different spaces. Let us know if we can help you get the right tile for your project.