I wouldn't change it for sale, nor would I add more beige. I think if you paint the wall in a contrasting color (red/blue/green) the room would look better.

Agree that lighter would be a good choice, but it looks like the rooms around it have rich color. A blue/gray a few shades lighter than the backsplash would blend nicely. I'd also paint the kickplates black to ground the cabinets.

First install under cabinet LED lighting clear around the room. Keep the counters fairly clear. Everything is lovely in the kitchen. If you do decide to do a backsplash, I would use an oversized off-white plain porcelain done in a running bond horizontally to keep with the clean lines. You will be very surprised at the difference that under cabinet lighting will make. Check out Ikea.