As a contrast but to prove the colours work together. We have grey units and cream walls, so yes go for it. I think if you have a darker floor and lighter walls, you'll keep the airy theme. I wouldn't bother with named colour paints from the likes of F&B etc, instead as you want to get the shade right, pick your tile, take the tile and a drawer front to any shop that will mix paint and that offers hundreds of shades and get the pale grey right. It needs to be a warm grey to work with cashmere. I think the phrase now is Greige ( Grey / Beige ).

I love the tiles and I don't think they are too busy. I might be biased, because I have very similar tiles in my pantry, which is of course much smaller than a kitchen, but still... My theory is: a smaller pattern merges into one, while a larger pattern forces your eyes to follow the lines, so the larger pattern is much more overpowering. Just my theory though. I'm hoping to prove it with the enclosed photos :-D I think they will look fabulous!

Something more interesting! There are such a huge array of tiles available that you can have something lovely. As the units and worktop are dark I would go with a light palette. Hexagonal tiles are lovely. If you wanted subway tiles you could lay then in a more interesting way such as herringbone (better with slim subways) or upright, like below

As mentioned by the others, having tiles and upstands together would look rather bizarre. I’d suggest removing the upstands and adding white or dark grey tiles. You could also add white tiles with dark grey designs to maintain the colour scheme that you’ve got going. Tiles would also be much easier to clean, and if you choose dark grey tiles, any stains wouldn’t be visible at all. I recently got my entire kitchen redesigned with the help of these kitchen fitters called Saturn Interiors. They took care of all the minor and major details, so I didn’t have to worry about any of it. If you want to, you could consult with them about this issue. I think they could provide you with better solutions too.