I would loose the formica backsplash. I wouldn't use natural stone for a backsplash. Just doesn't go w the kitchen layout. I'd use a ceramic backsplash that would go all the way down to your countertop.

That 5 inch formica back splash is constraining the best options, any accent material will conflict with it. I recommend keeping it very simple, maybe keep it painted but change the color, or putting in a flat uniform material. The best option would, for sure, be to replace the counter tops to a material without any back splash. Putting 2 different back splashes in the wall is not the best option.

What kind of flat uniform material are you suggesting or what color would you choose for painting? Thanks

I'd go with a tumbled light stone.