Many people with Carrara (which is similiar) have chosen Custom Platinum. It's a very light grey that tends to minimize patterns, if that is your goal. But, compare the color to your sample, as your tile may be different.

Most times we do not apply a spacer there, we use the backsplash as a support. But make sure this is level before doing this, otherwise you will have uneven tile at the wall cab! Here is a link that might be useful: Kitchen Remodeling Chicago

With a granite backsplash, you'll still have a seam so it defeats the purpose stated by that granite guy. Only time I see tile over a 3" granite backsplash is when they are done at different times (change in homeowners or you decide to add tile in the future). Most people getting new counters will just tile from the counter up.

Here is a link to google, how that backsplash should have been installed. There are some u tube videos too. I watched one video, where they used grout, between the countertop and the backsplash, and grout should not be used there. Caulking shud be done between backsplash and countertop. My backsplash is also caulked in all the corners, rather than grouted. Once you watch these videos and read these articles, you will see that your thinset was put on improperly, and thats why your tiles are falling off. Please read carefully. https://www.google.com/search?source=hp&ei=uI4VW7HdLszKjwTtrqSoAw&q=how+to+install+glass+subway+tile+backsplash&oq=How+to+install+glass+subway+tile+&gs_l=psy-ab.1.0.0l3j0i22i30k1l3.3755.12143.0.14244.41.29.3.9.9.0.173.3348.9j20.29.0....0...1c.1.64.psy-ab..0.41.3556...0i131k1j33i22i29i30k1.0.70wb9L5GlO8