Do you have to do a white curb?

My initial answer is that I like the shower floor to be similar to the bathroom floor. However seeing it with a white curb, I could be swayed to the white hex.

Yup, that chopped up effect is exactly what my husband is concerned about. Extending the floor tile is an option I suppose. I've seen it in one or two pictures - like the one below - but it doesn't seem quite right either.

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Most of the ones that look the best to me are actually curbless, like this one, which isn't an option with our setup.

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Here is one with a patterned tile and white-on-white shower. But that isn't exactly an exact comp for what we're doing since the floor outside the shower is more of a solid color.

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Jan is exactly right.

No, I read what Jan said to go now, get a remnant of honed black granite to match your floor to use as a curb, since you want a black curb. "And have something else for the vanity top," when the time comes to get that piece of stone. Get what you want for the vanity top. It does not have to have anything to do with the curb. The curb has to relate to the floor. It does not have to relate to the vanity.

I like the charcoal. do the curb in whatever your countertop will be, or pick something dark like I did w/my neighbors shower curb. got a dark quartz piece that matched the dark gray of the accent and floor tile.

( you can buy 4" or 6" backsplash pieces in any type of quartz and get them cut down to fit your curb)

on this one they went w/a black granite

Another option you could do, is both black and white. Do a rim of either for the border, and the other on the main portion. This way it will still blend w/the tile on the outside.

(this would be on the shower floor, not on the outside)

If you use a solid surface for the curb, water will not run out along the grout lines where the shower sweep can't block it.

I would do exactly what Jan said for the curb...that would be the most seamless

.The cut hexagon idea ???.not so much ...

Your bathroom is going to be great! Love what you described ...be sure to post pics!!

A shower curb should not have grout. Any " plain black" in any solid surface. Absolute Black granite is truly common as dirt. A few phone calls for a remnant in your area at a fabricator might take 15 minutes. Or simply hop in the car to a stone shop.

do not use cut tiles for the curb. as jan said, remnants that are 6"x5' are very common. they'll prob give it to you. (the one I used was a leftover and was 8' long. I used part of it for a shelf in the niche. another place you don't want any grout lines) The other option is to get 24x24 black tiles. This way you'll only have 2-3 of the 1/16" grout line on the curb. you can do 24x24 granite, or a black porcelain or even Basalt would be nice. Cut them into 24" long by whatever your curb size is,,,4" - 6".

The key is to have as few, or none, grout lines on the curb.