I agree--don't pick a tile that will fight with your granite. I love the larger subway tiles in neutral tones that Walker Zanger carries--the collection is called something like 5th Avenue, can't remember exactly at this moment. They're classic but not boring.

I would do a large format tile in one of the lighter colors of your granite.

Newport Heights Remodel · More Info

I think the grey glass tile you've chosen as a sample would look great. I would make sure the grout color was a touch lighter than the grey tile. I'd stay away from adding an accent color with your backslash. You can add accent colors through fun rugs, small appliances or kitchen towels.

Also, stay away from the small mosaic tiles. Too busy for such a beautiful counter and cozy kitchen, such as yours.

Hope this helps! Looks gorgeous so far!