That's an awesome idea. Lots of color, texture, robust surface for grime, etc. I'd glue 'em down using a siliconized latex adhesive caulk. (Siliconized latex caulk has more adhesion than plain latex caulk, but is much more removable later than pure silicon caulk. An example is a product called White Lightning 3006) Run a generous bead on the inside half inch edge and a zig zag down the middle then press firmly against the wall, checking that they don't shift. This will hold them fine but is also removable later with care. Just make sure the back sides are clean, for the adhesion.

lmao. what Jan said! Although, I had to help out my guys who did my herringbone wood floor. it's the starting point where everyone gets messed up. after that, it's simple. Look up how to properly start a herringbone layout and read it. you need to use a speed square at the end of your tile in order to get the proper middle starting point. much easier to illustrate than trying to write it out here. This is how I showed my guys how to start it. see the blue tape w/the two lines? you have to start on the middle after you mark your corner. that's the only way you will get perfect even cuts on both ends. this is how most do it, and it's not correct IF you want perfectly symmetrical left/right borders. All he's done is set the corner of the tile on the line. doing it like this will leave you w/one side smaller than the other: see how the sides of the window don't match? this is what you don't want. your tile guy should be doing a dry layout in order to determine where he starts so he doesn't get this look or these tiny triangles. Again,,,see how the ends don't match below? the right has longer tiles than the left edge. that's because of the way he started his first tile. And don't do these vertical tiles for your edging. get proper bullnose tiles, pencil liner or a Schluter edge. This is a layout board of my herringbone for my shower. took a few hours in order to get this almost perfect. since this was an odd size, and the tiles were even at 3x12, it couldn't be perfect. the right bottom corner triangle is the only portion that doesn't match. luckily, it's not readily visible! Even the subway tiles are perfectly matched. this layout took hours to get exact, even around the niche. 2x6your 3x9 will be 1/3 larger. 3x9 is a good size for a backsplash. this is a regular 3x6. again, a 3x9 will give you 1/3 longer.

they sound interesting enough to me, being crackled and having variation. larger size might work..what size you consider? Gray is already considered dated lol. Makes no sense to me personally as all this dated thing is a new concept I'm still struggling with-how a color can be dated? but in terms of what happens in trends etc-it's on its way out, yes. they move into warmer tones. they're still into greiges for now to bridge between things a bit. white is becoming big as a neutral. wood stains are making a big comeback. this update on trends can go on and on but i'm sure you can find thousand threads here discussing it so i'll make it short. if you're really worried-it might be you're simply are not attached to a color enough. which is okay, really. then pick off-white. off white is pretty. Even very much so. I like both off whites and grays(I do have preference for much warmer grays though) so I have off whites and warm grays. And many other colors too since I love them too. I commit by choosing something of course,-but it's fine since commitment, paradoxically, is a road to freedom:) But I admit I was also worrying when choosing..well choosing everything except for stuff like toilets etc. Of course one worries, it's a hassle and an expense and you want to love it in the end. So. Try to worry less. If you can remove "dated" from the equation- great. Go with your heart's desire. If no-then ok, take it into equation and don't do gray. Worry less. You did a great job on everything else, so no reason to think your backsplash won't turn out well either. It will.

OH BOY. I'm sorry I know you must be unraveled, but realistically it looks more like the counters dont go with your kitchen as they are brown tones and everything else looks black white and gray. Why did you leave the granite backsplash up? that would help minimize it a bit I think.. We need to see the whole room.