Keep it simple. One backsplash for continuity, especially in your smaller space. The white is a bit stark with your cabinetry. The mirror is going to be reflecting pots and pans, and if installed in the whole kitchen, the undersides of the cabinets. Perhaps consider something in a mother-of-pearl with your countertop colors? Reflective but not too stark.

I would run one backsplash all the way through. And in a solid which picks up some of the color from the countertop. Perhaps a darker gray.

Agree you need to keep it simple. Love the white mother of pearl, but think the white may be too stark. It also feels too busy for the granite. Look for a simple 3 by 6 subway tile-choose the lightest color from your granite for some contrast with the cabinets.

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I am going to suggest my all time fave... porcelain subway tile in a running bond horizontal pattern. Or for a switch up you could install it (after the small granite backsplash is removed) end-on-end side-by-side vertically.

You could go with a very pale color If not choosing white & grouting with white or if using white tile grout with the beige in the granite. The important thing you must do is to install LED under cabinet lighting. You have a beautiful bright kitchen & the subway will add the timeless, classic touch to set it off.

Keep it simple.