I recommend matching the tile. But honestly, the gray of your tile looks much more blue than the gray elements in the counter -- are you sure it's the right gray?

Decide on the grout color later. If you like the appearance of the dark lines between the ungrouted tiles, go dark. If not, go light.

In the first photo the colors appear perfect, but not in the second. Which one is more accurate?

You do not need the "busy" of sharp contrast grout with your subway/ granite. If you'd like to acknowledge the deeper gray in the granite, select a different tile for the splash. Perhaps a multi gray slate subway. Your tops appear to contain both light and darker grays. Truthfully, the most DOMINANT tone in the counter appears beige in the close up photo, and acknowledging that may get you the smoothest result. When you "reach" to pull a secondary tone from a busier top such as granite, you're often disappointed. I would wait on the decision of any tile and bring home a few stone selections, slate, travertine, .....and then decide. Slap some paint on your splash, clean up, and take your time. I think you're reaching ....and the result may be a disjointed appearance with the granite. If stuck on gray....I'd try something that pulls in several of the gray tones ( link below)....and sample first after with another more beige selection as well before any final selection.

http://www.google.com/shopping/product/10304263669660365279?q=slate+wall+tile&hl=en&gbv=2&prmd=ivns&prds=paur:ClkAsKraX-I21ACwku_mo5r3HoIoxax1A6FEr7W7Qw8XX_dpf5Zv8BIPx40eKeqvjDilmNjhf_NVzWkBEGKjO_4YvWgqsu3xVYnmO33-_uNSrBA4QgW2zxkEfRIZAFPVH72ud-DV52r8B9lEGV8mH-pBR_eDgw&sa=X&ved=0ahUKEwj15-eCpeDJAhVCSSYKHRowBj04KBDyAghMMAs

A very dark grey or even black tile would look great! Also something with texture, like the glazed bricks from Waterworks or Ann Sacks.

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Also, remember that the spacing between tiles is predetermined by the type of tile. Straight, rectified tile is set with very thin grout lines, while handmade tile requires larger thicker lines. You should show your tile sample to the installer for his or her recommendation on the width of grout before you purchase it to make sure you will like it.

The tile looks a bit blue due to the yellow background. Also, the yellow reflects off the granite giving the granite a yellow look, as well. The "color" of an object depends upon its surroundings.