Perhaps you could follow MB's advice and match the sofa colour for the splashback, then introduce the teal blue with accessories. I like the following images showing those tones together. You would need some more wood items to add warmth to the glossy white kitchen though. Do you have a picture of your sofa handy?

In or out of date just go with what you love! Colour is easily added and changed with accessories. But a splashback can always be altered later on as well, although at more expense. I really like the photo splashbacks. We're thinking of putting a picture of my fathers family farm behind it but I've seen lovely ones with underwater shots, fields, even a family shot. Go nuts. If you don't like it, change it later.

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!

I would go for high gloss black tiles. I know you said natural light is low but you can get black tiles with such a high gloss they reflect a lot of light. The black would look dramatic.