None of the above. Go with a bright white grout that matches the white tile. Contrast grout gives the tile a graphic look, which you already have with the black accent tile in this mosaic pattern.

I agree with white. Black may take away from the accent tiles to pop.

I'm going to disagree w/the white choice. The lighter grays visually disappear when viewing and are a bit easier to keep clean.

White grout in a shower or on the floor is a PIA to keep looking white.

Dark colors in the shower will lighten because of hard water. Ask me how I know this. I have Charcoal grout on my floor tiles.

The grays will be a nice choie.

In fact, I'd do the same gray for your wall tiles.

You can see mine here. I did Mapei Warm Gray on the white subways, and the black/white marble in the niche.

Here's Warm Gray on a close up. it almost looks like white, but has a warm/grayish tone to it.

the black tile floor got Charcoal and has lightened in spots.

(The downside to dark grout- if your tile installer doesn't know how to grout w/dark grout, ie,using too much water, you will get light spots and washed out areas. Dark Grout takes a lot more time to install and to clean up. )

The Warm Gray against the white is light enough but still lets the pattern show through. Frost is fine, but again, white against white is going to look like a solid white sheet, and in a shower white grout will discolor

The warm Gray (Mapei) will be slightly lighter than what you see here

your tile w/a darker gray

LIGHT GRAY AND WHITE

https://mariakillam.com/best-grout-colour-for-white-tile/

But, to be sure, just do a sample piece w/white, the gray and the darker one. use scraps of tile glued to cardboard or wood or cement board and test out the grout colors

grout color makes a huge difference.

verbo, it's perfectly fine for floor application.

"Indoor and Outdoor friendly, first quality floor and wall use"

I would do something right around #3--it will look dark against the white and light against the black, which will make the design pop. We have white hex and used Custom's Pewter with it; Delorean Gray would have worked too for something a touch lighter. For Mapei, similar colors might be Pearl Gray or Silver. Definitely wouldn't use black or white.

@Beth, thank you so much for your photos and input. On the photo I posted, Warm Grey is actually #4, and Frost is #5. We did Frost for our upstairs bathroom and the color didn’t wash out the tiles. I love your bathroom. The niche is flawless.

@artemis, I tried Pearl Grey but it read too brown for the tiles, and Silver was too cool/blueish tint. Thank you though! #5 is actually a very light grey, not white. My bad for not clarifying

A light to medium gray is always a good choice. Enough contrast to show the shapes, but not enough to make it a harsh gridwork. Something like Mapei Cobblestone. Or Warm Gray, if you prefer a bit lighter. Nothing darker.

As a FYI educational point, this is the rating for the Octagon and Dot that we sell. Not rated for traction for wet floors. You have to be careful to check that with all bathroom tile choices. Different brands produce different products. We sell a black and white hex, or a black and white penny tile, that IS shower floor rated.

https://digitalassets.daltile.com/content/dam/Daltile/website/resources/products/sales-sheets/octagon-and-dot/DAL_OctagonDot_SS.pdf

Compare that to a tile that is rated for showers, or even pools. https://digitalassets.daltile.com/content/dam/Daltile/website/resources/products/sales-sheets/keystones/DAL_Keystones_SS.pdf 

Black or whaite grouts are both hard to keep looking new I agree #3

I pulled the one they sell at Home Depot and read those specs. It said it was ok for floors. PEI 02. Powder rooms and light foot traffic. low water absorption . 0.5%. This tile will scratch with heavy foot traffic/dirt-grit or shoes. In a shower, it should be ok. They don't have a COF rating on it. They wrote this on their specs page:

A newer standard, called DCOF, is an evaluation of the COF of a tile surface under known conditions using a standardized sensor prepared according to a specific protocol. Measurements are made using a tribometer, under wet conditions using a 0.05% sodium lauryl sulfate solution to establish a thin film as would be present when a slip occurs. Because many variables affect the risk of a slip occurring, the SCOF and DCOF measurement shall not be the only factor in determining the appropriateness of a tile for a particular application.

The one that OP had looked like a matte finish (the black dots are glossy) The grout should provide enough traction.

However, to be sure, throw some water and soap on a few sheets and see how slippery it is.

4 or 5...

I posted the Daltile specs above. And the HD specs agree with the ones I posted.

https://www.homedepot.com/p/Daltile-Octagon-and-Dot-Matte-White-with-Black-Dot-12-in-x-12-in-x-6-mm-Ceramic-Mosaic-Floor-and-Wall-Tile-1-sq-ft-Each-65012OCT21CC1P2/202195275

The tiles we got are from Centura Tiles. https://www.centura.ca/sites/default/files/images/old/carpet/product/tech-doc/basic-hex_eng.pdf

I don’t think it has a rating on the soecs but I know our interior designer and contractor checked our tiles beforehand if it was fit for a shower :(

These are porcelain and look to be fine for a wet area. not everyone can afford made in america anymore.

Please, do not go there. Daltile is North America's largest manufacturer of porcelain and ceramic tile. None of it is "unaffordable." It is all very moderately priced. The largest expense in any remodel is not materials. It is labor.

#4

#4. Here is my hex tiles in my bathroom with a grout color similar to #4. My tiles are matt porcelain.

Thanks cpartist, looks great!

PEI is not DCOF. They measure different things. One measures resistance to abrasion, i. e. foot traffic. The other measures the slip resistance of the tile when it is wet. A condition that tends to occur a shower. This is why it is important to use a tile with an actually tested rating of .42 or greater.

Magnolia, yes, I'm aware. That's why I said it was ok for light traffic and would scratch easily. I was just posting the specs on the tile. I clearly stated that tile I was looking at had no DCOF rating.