I found this image with a white backsplash and I do not care for it. It seems like too much white. How dark are your gray cabinets?

A white 2 x8 or 3 x 12 subway in a match to the counter background will be lovely. The reason the photo looks cold (above) is the result of a skylight in the room. I'd guarantee it.

Also lovely.....in white ( check your local tile venues for similar with plenty of white in them) . These are best when your cook is on the island if there is one. The scale of tile and tones within are small and tight enough to be beautiful with "Ella"

https://www.mineraltiles.com/haisa-light-marble-split-face-mosaic-tile/?gclid=COKYjunVzc8CFQMMaQodBQYEsw

The cabinets are much lighter; almost taupe in certain light. No pictures as they have not been installed yet. I was thinking of subway tile but not sure how white or if I should do beveled

No to the bevel!! Wait until all cabinets and counter tops are installed . Go to a TILE local source, ( not a big box store, better one specializing in TILE) and bring home SAMPLES. It is not necessary or even advisable to pre select a splash. It' the last thing to be installed in a new kitchen. A clean, painted wall can survive for MONTHS in fact. This is a far better route to take than a mistake, and a subsequent result you are not happy with. Tile is a lot easier to install, than it is is to REMOVE.

Painted glass has depth and is really easy to up keep.

http://www.daleallenspiry.com/index.html