Beautiful cabinets and backsplash! I would probably go with a more neutral color to really make the backsplash stand out, but if you want a deeper, richer look then one of the olive green or earth tone colors from the slate would be perfect.

Your friend should tell you which stone yards he/she works with so you can go look at the slabs (with a cabinet door with you to hold up against them) and take home samples of the ones you like to see in your lighting. Given the warm tones in the cabinets and floor, creams or warmer whites would probably be better than cool/stark whites or grays. Unless you want to go dark - then a black would work well too. It all depends on what your style is, the colors you like, and what you are looking to achieve. Do some googling and searching on here - warm wood kitchens - and see what you like and strikes your fancy. While getting ideas from pictures is great to steer you in a general direction, slabs vary greatly in person so you MUST see everything in person or run the risk of being hugely disappointed in what you get vs. what you *thought* you were getting. https://www.google.com/search?q=oak+cabinets+with+granite&client=safari&hl=en-us&prmd=isvn&source=lnms&tbm=isch&sa=X&ved=2ahUKEwjCyZLZ_eDfAhXIwlQKHd_jDnwQ_AUoAXoECAwQAQ&biw=375&bih=544

Don’t panic…I just finished a living/dining room with high ceilings and it came out so gorgeous. B.M. Mesquite. Looks wonderful with Hale Navy. Unfortunately the inspiration photo has used purple, but I hope you see the possibility.

Pick out colors or whites like you want. Paint on poster board, or buy the peel and stick color patches and put on poster board. Leave a white border all the way around the poster board, so it doesnt clash with the color you have now. Since you want the whole house the same color, then pick a color that goes in your kitchen with your cabinets etc first. Then try it in the rest of the house. The color in there now, does not go with your cabinets. It has way too much yellow in it. I would look for colors that have no yellow hues.