We have installed wallpaper behind glass splash backs on many occasions without any problems, the glass usually being attached by a thin beading of clear silicon applied around the inside perimeter of he glass, then fitted the day after the wallpaper install. MOST importantly the INSIDE of the glass be kept perfectly clean on install as even fingerprints will stand out

I would get in there to enliven up the space without taking away from the clean lines. You don't do that by repeating more of the same. You make the rest of the kitchen, with all its weight and clean lines play into something not the same. I would suggest you look at a gold leaf look ( ie with a little texture in it. Obviously not actual gold leaf) and put the most vibrant magenta pink/red that you dare in a horizontal line about 2 inches wide and going the full length of the area. Just very well executed paint. Make it above your average pot size so it does not disappear behind pots and pans. That way every time you will look at that place in your home and think Oh Yeah! Also, if you would rather .... make the coloured line turquoise.

We did pressed metal splashbacks on a display in a kitchen showroom I used to manage, and as such many of our clients opted for the same look. Powder Coated is definitely the way to go. It stands up really well for durability and is in fact relatively easy to clean compared to many splashbacks. Often people think that glass or stainless steel are the easiest for cleaning, but due to being such a flat reflective surface they show up every splash and if you're going to clean them you really have to clean the full length of splashback. The textured surface of the pressed metal means that it doesn't reflect the same amount of light so you are able to get away with cleaning it less often, and you can also get away with just cleaning the dirty area rather than the full length. The biggest difficulty we found was getting the splashbacks installed as there aren't really any tradesmen who specialize in fitting pressed metal, and those that were willing to cut & fit it were concerned about what would happen if they damaged the paintwork. We had the panels cut to size first before they were powder coated to minimize the risk of chipping the surface.

I agree that it's hard to choose the style without seeing the rest of the house but that a charcoal colour (same as the island cupboards) would tie in best with the colour scheme you have. Depending on the look of the house you have a lot of options to choose from and a lot depends on personal taste or budget. Glass is easy to keep clean and is a modern look if you are not wanting to draw attention to the splashback. Mirror (plain - modern or distressed - character) is lovely if you have something nice reflected in it. If the kitchen is messy though, it doubles the mess. Subway tiles (regular or irregular, tiled in brick format or herringbone) are always a lovely classic choice - but be mindful of grout issues. Arabesque or patterned tiles add more character if you're after tiles with a wow factor. I personally love stone, marble or quartz for an elegant, timeless look and in a charcoal or grey with veins I think would look stunning with the lamps as well as tying in the white and grey cabinetry. You can also do marble tiles that are a little less exxy than a slab although in the end I was surprised that the marble didn't cost much more than the caesarstone. Choices, choices!! Good luck. Your kitchen looks lovely!