That granite is beautiful - it looks marvelous with your cabinets. Maybe a light gray glass subway or plain whisper-light grey or white subway. Or maybe a very, very soft green glass subway. Whatever you choose, make it very subdued -- something there but not really, you know?

Take a look at Fireclay glass tiles: Glass Colors | Fireclay Tile

ETA: Sorry, missed the part about not liking subway. But I still think it needs to be visually quiet to let the countertop have the spotlight.

I agree to find something a bit more interesting that subway.

How about one of these...

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a two inch square creamy tile if you don't like a subway.....I'd keep it simple/ not a shaped tile/stay light in color. You have the correct amt of detail with counter pattern..style being waterfall down the sides...the frosted glass cab.......a smallish run in each of the two areas. Subway would be my choice but a small square tile can work nicely. Have you thought of looking at subway tiles that have a tweak like size of tile.....maybe a little more glossy ...maybe some tint to the grout color? Such a nice install, so far. Lookin good.

I think a gray back-painted glass would look great. It's more common in very modern kitchens, but I think it would pair well with your counter. Uniform color and minimal seams would let your counters be the star, while not being at all boring.

Source: https://www.cbdglass.com/product/kitchen-glass-backsplash-bspl30/

I like that idea