A pale warm stone coloured splash back would work with the units and complement the rich wood. Have you tried standing one of the floor tiles up against it to see how warm neutrals would look?

Hi La, it comes down to personal preference if you're going for a fresh look. I quite like a gloss backsplash. What colour are your units? I would also recommend getting a few samples to compare to your worktop, not all white tiles are true whites. You might find some look more yellowy next to your worktop. Here are a few inspiration images from Pinterest of matt & gloss.

Thanks Sonia and Louise. I was initially going to tile to just below the extractor fan but to ensure of no splashes on the wall, I felt I needed the tiles to be higher. In the end I went for a feature wall of tiles but removed the upstand and splashback. I've still to put some reclaimed scaffold board shelves up so please ignore the copper brackets you can see in the picture. They're sitting on my worktop at the moment.

Oh, paint it. Personally I’d paint it a dark grey similar to the worktop so that the line between the two disappears, if that makes sense. It will tone well with the floor and make a lovely backdrop to simple accessories. You might need a fair number of coats, but I have had something very similar in two houses now—including behind the hob—and it has proved very resilient and easy to clean. Also, the wood provides a nice surface for sticking stuff to as the seasons change. I put tiny little Christmas trees (card decorations, really) on the border and this time of year. In the past I’ve stuck everything from ceramic plaques to pretty paper plates.