I think the whole thing done with the mosaic tile would be beautiful!

I find mosaic tile was a very strong trend in the past. Unfortunately it looks tired now. If you love it, great, otherwise, keep looking.

Dated. Look for a unique shape such as fish scale for a bit of interest or arabesque and possibly do a grout in a deeper tone than tile.

Some options.

Basalt black subway.

I find it way too busy! Go for something more simple, as the other poster suggested.

Too dark with the dark counter. I would go for a white tile and use the mosaic as an accent stripe.

https://www.belktile.com/blog/neat-things-to-do-in-your-home-with-copper-mosaic-tiles/

Maybe something like this copper mosaic tile.

^If you do have copper brown in your granite, pull out the copper color and do something striking like the above backsplash.

I don't see copper brown granite in your pic. It could be the lighting. The granite looks black to me. If you do have copper brown granite, check your lighting first so when you do find a (much better) tile for your backsplash, you end up with something that works. Stay far away from mosaics.

If the countertop is actually black, like it looks, then work with the shapes like Flo shows. Fireclay Tile has fabulous tile. Take some time to explore their website.

Definitely not that mosaic. It reads too dark, and doesn't work with the cabs or counters. It also has different colors, different types of tile, and different shapes, so it has "too much going on." If you like the look of mosaic, it's better to pick a monochromatic one, with 1-2 colors total and all the same type of tile. This will result in a more harmonious look to your kitchen.

Definitely not the mosaic, too dark and busy, a past trend.