I like your cooper idea. Lowes carries tin ones give them a look. If going more traditional kitchen. It's not a modern look.

i second the bevelled tile.

i would put that pretty copper tile on a plate stand and use it as decor instead of attaching it to the wall.

Hey there! Not sure if you have ever considered going with a bit more of a modern/rustic touch, but a reclaimed wood backsplash could be really pretty in your space. There are a ton of different types of wood options, but there is something called grain eroded wood that has a really cool texture (definitely a conversation piece) - and it looks super cool as a wall accent. Here's a little picture of what it looks like in rough form and also one of an installed piece. There are a bunch of different levels of erosion to choose from and it can be stained any color (or left natural). If you are interested, let us know and we can point you in the right direction!!

I would also have to agree with the white subway tile, beveled or not, it's a classic look that will not compete with your counter tops. Another options is a tumbled travertine. More of a rustic look, but still very traditional. Either option can be accented with a neutral colored glass for a bit of personal style.

OK yet another way to go. My first thought was a subway tile. You could also put a 2+ run of the same material as the counter and then use beadboard pained a gloss white. It would give a traditional look that goes with the copper sink, does not fight the coulours already in place, and is easy to install. It is also very durable and easy to care for (contrary to common thought). You can always wash it down and paint over when needed. With the right quality paint is lasts along time.