Overall I think the color scheme is working very well!

My favorite is the bathroom floor gray-ish tile (it has kind-of a concrete look, which I like) - I would actually consider doing the shower and bathroom walls with that tile as well (in which case, I would make sure other elements in my bathroom such as the countertop and wall paint are white).

Here is my currently-remodeled master shower area - the shower walls has a very similar tile, I've used the same tile for the niche, and I kind-of regret not using the exact same tile for the bathroom floor too (ended up using the same tile collection, just different (darker) color):

I'm not a fan of glossy tiles, but if you like the glossy-ness - you should definitely go for it, the colors work together very well. It looks like this tile is *huge* though (is it 24"x48" or 36"x48" or something similar?...) - it's likely very heavy and may be a challenge for your tile installer to work with (had a similar issue with 24"x48" tiles I've used for shower and bathroom walls on a previous master bath - turned out stunning, but a complete nightmare for my contractor to work with).

I have to admit - the tile that you chose for your niche is my least favorite... to me, it's a bit flower-y looking, so perhaps a bit childish?... - not a great choice for a master bathroom IMO, but again - if you're a fan - you should go for it, color-wise it looks good and works well with the other elements. I would personally re-use either the shower tile itself, or the shower pan floor tile for the niche.

You haven't mentioned things like countertop, wall paint and cabinet style-color - but since the color palette you chose is pretty neutral - it would work well with a bunch of things (for example, I can see neutral colored, bold colored or natural wood cabinets easily working well with the rest of your design elements).

Good luck!

What kind of vanity would you suggest in terms of color?

I prefer vanities with gray tiles.

Hi Simone Fields, since you chose such a neutral color palette - the possibilities are truly endless! :)

I recommend you will look through Houzz for inspiration photos which have material selections similar to yours, and see if any vanity in these photos is looking particularly good to you.

Some options:

Natural wood (white oak in this case): https://www.houzz.com/photos/tuckborough-urban-farmhouse-transitional-bathroom-minneapolis-phvw-vp~176426288

White: https://www.houzz.com/photos/our-work-transitional-bathroom-toronto-phvw-vp~84048113

Gray: https://www.houzz.com/photos/spacious-and-open-bathroom-mercer-island-transitional-bathroom-seattle-phvw-vp~145085347

Bold color (e.g. Blue): https://www.houzz.com/photos/hingham-shipyard-transitional-bathroom-boston-phvw-vp~134249739

One photo I've recently seen at Houzz is my current favorite when it comes to cabinet colors, and it's this Smoky Blue (?) color:

So I definitely recommend to keep looking - once you'll see it, you'll know it's the right one!

Also pay attention to the cabinet door style (shaker is always a safe choice, but you may choose something else to your liking), matching countertop and hardware (pulls, knobs, faucets, mirrors, vanity lights, etc.) - note that on every photo I included here, there's a white countertop, which is what I'd recommend to you as well - maybe with some delicate grey veining, if you wish, ideally one that matches the grey in your shower tile veining, or your gray-ish floor tile.

For hardware - I'm personally a big fan of oiled rubbed bronze (for a more traditional look) and matte black (for a more modern look) - but again - tons of options out there, keep looking and see what looks best to you.

I would not emphasize the niche and I dont think the gray floor tile works with the penny tile and wall tile.

Cpartist. What would you recommend?

I know that Penny tiles are very in right now for shower flooring. However, in my opinion, all you are doing is creating a lot of areas to clean. I used either that gray tile, or something similar to that that Floor and Decor in my hall tub/shower. Hubby really wanted an industrial look. Then I used a gray toned tile that was dressier in my niche and counter, backsplash, and then my flooring is a grayblue/brown wood look tile. Another reason that I did not go with a glossy tile is the fact that if your water is at all hard or calcified, all of those dots will mar the shiny surface quickly. I love pretty bathrooms, but I always think about keeping them clean first. Our house is too well lived in.

This centerset bathroom faucets are perfect for your bathroom! I have been using it for two years and the quality is very good. I recommend you to use it.