Removing the 4" will give a cleaner more uniform look. IMO I would take the tile to the ceiling . It will finish off the window wall quite nicely.

Your cabinets have pink undertones. So does travertine. Travertine wouldn't work with either the cabinets or the granite.

Plain cream crackle ceramic 6x6 on the diagonal. It's not the overused white subways, and it ties the granite to the cabinets without reinforcing the pink tones. Without the 4" splash.

Your granite has a lot of movement and pattern - I wouldn't add another stone, but look into a ceramic tile for your splash - like what Sophie has suggested. Also, Travertine is not a best choice for a working kitchen. Even with sealing, travertine is porous and can be a nightmare behind the cook top and sink. If you go with the glazed ceramic subway tile - taking it to the ceiling is not a bad idea. I would remove the granite 4" splash, too.

Completely agree with Sophie & Michelle

Tiles to the ceiling would be a bit too much. Would leave back splash as is -- single 4" - 6" row of tiles or at least stop back splash at the bottom of the overhead cabinets.

Have you considered pressed metal wall or ceramic wall art for the blank ends of the overhead cabinets or perhaps really colorful trivets

http://thumbs.ebaystatic.com/images/g/TUkAAOSwT4lWTUr7/s-l225.jpg

-- and perhaps even something for the side of the kitchen island?

https://img0.etsystatic.com/010/0/6764584/il_fullxfull.425175554_8uo6.jpg

https://s-media-cache-ak0.pinimg.com/236x/1a/fc/3f/1afc3f5be8ea8e9cd68e968e3a2e7ae5.jpg

Listen to Sophie.

Taking the tile to the ceiling would be the nightmare. Where do you end it? How are you going to tile around the crown molding at the top of the cabinets?

Remove the 4" backsplash, and then tile between the granite and the bottom of the upper cabinets. Use a handmade porcelain tile in a 2 x 4, 3 x 6, or 4 x 8. A 6 x 6 offset is also a good look for handmade tile.

Try a large format tile.

Larry, we see so many dilemmas where the OP is devastated that their travertine looks pink against their granite. You are so lucky you asked here first.

Larry,

Go to a tile store, borrow a few boards or sample of simple ivory tiles. Handmade is lovely, you'll get some waviness in the texture, a crackle is nice, in ivory. The grout should match. It isn't brain surgery, and it's a BACKSPLASH. All of these dilemmas of "tile nightmare" are a result of someone making more of it than a splash was ever intended to be. Your granite and cabinet tone dictate and you already have great advice above. Go get some samples as online is not for everything.....ps stay away from beveled edges.