Embeth, Is there a reason why you do not want a plain white or gray backsplash?
Are you afraid a solid tile will look too plain/boring? Here is LG Aura (a "relative" of Karis) paired with an off-white herringbone backsplash. A light gray grout was used with 3 x 12 subway tile. You may not have seen many pictures of a quartz countertop paired with a natural stone (e.g., marble) because sometimes the two materials (real stone vs. manmade) compete with each other. Maybe you could look at some pictures of the solid tile in different patterns to give it the beauty you are seeking. There is a reason why so many pictures of patterned countertops are paired with solid tiles--IMHO, there can only be one major pattern in the fixed kitchen finishes to be timeless and to avoid looking too busy. Even you are questioning whether marble and the quartz are too busy together, so maybe your gut instinct is trying to tell you something. When you are trying to pick out finishes for a kitchen, it is hard not to fall in love with so many beautiful individual items. However, if you were to put them altogether, you might find that they are competing with each other. Sometimes it help to think about what do you want to be the star in your kitchen--counters, cabinets, or backsplash. Then enhance the main focal point with more supporting items. The backsplash is the backdrop for your kitchen. Most folks put some things on the counter to add finishing touches and color. Remember you are striving for an overall, cohesive look. You want to say, Wow! What a beautiful kitchen." instead of having the pieces fight for your attention. And you want the finishes to be ones that you can live with for a long time since they are so expensive to change.
Karis is a beautiful quartz for a countertop. If you want something more than plain tile for the backsplash, you may want to think about using the countertop material for the backsplash. (Hard to know what to recommend without seeing the space.) If you consider this option, be sure to hold one piece of the material vertical to the horizontal plane of the countertop. In other words, when selecting the countertop/bashsplash, hold them as they would be installed--horizontal counter; vertical backsplash--instead of laying one on top of the other. Orientation can make a big difference. If you are near a place with the large slabs of Karis, take several pieces of marble with you and then view it. Sometimes I find it helpful to take a picture of the combination. For some unknown reason, I can spot it better in a picture than in person. Good luck with your kitchen. I know the Karis countertops will be beautiful!
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