Sounds beautiful. Light gray glass tile would look lovely. A herringbone layout or arabesque shape would add interest and bump up the design beyond the boring white subway look.

If you like the subway look - go with a longer tile (3x12 for example).

http://www.discountglasstilestore.com/3x12-glass-subway-series-light-gray-sale-price-6-89-sq-ft/

You have chosen an amazing granite countertop! It's a versatile stone, so you can use Aspen White Granite as a backsplash, too. Another option would be to go with white subway tile - a herringbone layout. We've compiled a list of different Aspen white granite kitchen countertop designs, so you can check out different kitchen combinations - both white cabinetry and dark cabinetry, as well as different types of backsplashes, with Aspen White granite countertops. Do let us know about your final decision. Good luck with your work!