I would do a darker grout to pull out the color in the stone. Also, it would be visible and not blend in.

I don't think I would like using a dark grout on the shower walls and bath floor and then a lighter grout on the shower floor - particularly when it is off color from the wall grout as much as the first three choices are. I would keep it all the same.

Of the three choices I would go with the lighter one "Buscuit". On my monitor the tiles appear to have more lighter grayish tones from an overall perspective. The lighter grout also appears to work better with your proposed wall colour.

Graham

Light & thin 1/8 grout but if it's not too late--rethink the shower walls. The wall tile looks extremely modern while the shower floor looks traditional. They don't compliment each other even though the colors are similar.

What are you going for as far as style?

I agree with leelee. The tiles don't really go together. Have you talked with a designer or a showroom for tile sales?

Use a medium gray on the shower floor--none of the ones you posted look right, but that could be my monitor. The one on the left looks pinkish, middle yellowish, and the right is too light.

And yes, leelee is correct about the clash in styles. Either select a different shower floor or wall tile, depending on which style (modern or traditional) you are trying to achieve.

Thanks to all who have commented. It is not too late to change our tile, but we had worked with a tile showroom and they didn't raise any issue with the tiles going together. My husband loves the wall tile so we need to work off that. I see from pics on Houzz people using a square tile on many floors with this kind of floor tile (looks like 2x2). Our main concern was finding a floor tile that was a bit rough to provide traction on the floor. Can anyone provide any recommendations as to floor tile to use?

As for the style we are going for, I feel the wall tile makes it contemporary, but if there are suggestions to temper that and make it a bit more timeless, I would welcome same. Thank you!

No way would I put holey, porous, high maintenance, travertine on a shower floor. Even sealing it won't keep the dead skin cells and soap scum out of it. Without adequate ventilation, and precision waterproofing under the tile, it will be a gross mess shortly. Even with that, it will eventually be a mess.

I don't think the two tiles go well..If you look for linen tiles, those who used them in the shower, used pebble tile on the floor

Check out Glazzio's Carnival line. Comes in two different shapes and three colors, all neutral. It has a rough texture for non slip.

http://www.glazziotiles.com/products/CARNIVAL%20SERIES.aspx

The shower floor tiles need to be small so that they can be laid to drain correctly. The travertine mosaic you are showing is for a backsplash. If you want the modern tile walls, look for small 2x2 squares that compliment the tile but in a solid color. You could repeat the floor color in the niche or as an accent strip.

It depends on the way the inclination is...you can have large tiles on the shower floor. I've also seen some really nice shower floors done in 1" by 4" stacked.

Here are a few ideas.

We used Daltile Fabrique in Noir for our large shower. It is also a linen porcelain so that the floor has texture and is not slippery. The floor tile is a 2" X 2" mosaic with the 12" X 24" larger format for the walls. Using the same tile for the floor and walls gives a modern and consistent look, and obviates the need to choose different grout colors.

http://products.daltile.com/series.cfm?series=228

Thank you all for the guidance/comments. I am a bit confused - is not the tile in suzyq53's first picture the same tile as we are considering (it is used in entire shower including floor)?

I always try to match up with the Main color of the tile or stone so you don't get a checker board affect. This way it tends to make everything blend.