Since this is not a new build I think you should wait for it to all be installed. Then you can bring samples to lean against the wall in your lighting.

River white granite is mostly gray and white and tiny flecks of berry. In ANY case and as with most all granite containing pattern you have already chosen the star of the kitchen, and there can be only one. The backsplash should be subdued, and you will find after counter install that a plain and simple subway in white in 2 x 8, or 3 x 12 with matching grout is going to look best. Virtually anything else will look busy. Or you can REPEAT the granite as the backsplash..... with a no grout advantage,