Typo, that was supposed to be Silestone quartz (not Sistine).

Pick a color that goes with your whole house pallette, especially the other common rooms.

For paint, you’re going to have a sample a few colors in the space. But I’d be looking at different shades of whites.

In terms of backsplash, I don’t think I’d do marble since it’s not going to be the same pattern as the countertop I feel like it might get too busy.
But you can, see if you can get some more of the countertop material and use it as a backsplash, although that might not either be the best option since it can scorch from the heat of the stove.

Here are some backsplash suggestions:

https://www.tilebar.com/calypso-bianco-8x16-honed-banswara-white-marble-with-brass-tile.html

https://www.ziatile.com/products/white-2x8-cement-tile

https://www.ziatile.com/products/sky-light-2x6-zellige-tile

https://www.bedrosians.com/en/product/detail/cloe-tile/?itemNo=DECCLOWHI28G

here is repose gray also...they leaned to a white for the adjacent surfaces. I think your island makes the cabinets appear blue green almost.......but I wouldnt extend to a color for the walls.....just a muted white not as white as the island top stick w white for the backsplash too.

repose gray show w white..not boring due to the design elements. You have plenty going on in your space ..search whites for walls and backsplash I think. your cabinets look nice. and the floor stands out so keep it simple .

Monochromatic Luxury · More Info

This link might be some help. Scroll down for suggestions of whites with Repose Gray.

Kylie M Interiors - Repose Gray

BTW, Repose Gray is a favorite. We used it on our exterior.

Beautiful cabinets.

Paint your walls repose grey. Run a 4" strip of your countertop material as a backsplash. Get a stainless steel splash to cover the wall behind the range.

What do you think of beadboard as a backsplash?

https://www.westelm.com/products/beadboard-peel-stick-wallpaper-d16222/

https://www.homedepot.com/p/EUCATILE-32-sq-ft-3-16-in-x-48-in-x-96-in-Beadboard-White-True-Bead-Panel-975-759/205669196

https://www.wayfair.com/home-improvement/pdp/e-joy-106-x-24-flexible-fluted-semi-circle-wood-shiplap-wood-wall-paneling-3d-wall-paneling-for-interior-wall-decor-ejoy9829.html