I'm not a niche fan. Lots of work for little gain and they're rarely done right. Siliconed solid surface shelves can't be beat.

Well, here are my new niches which came out great.

I find niches important, but yours were not well done.
I would demand a redo.

I would post this question on the Tile Forum Advice Board. The pros there should be able to give you the best advice on how to proceed.

We DIY'd our kids/guest bathroom with the help of these guys and gal's. Very happy with that bathroom, including the niches, 9 yrs on:

Our niche with marble

I think I’d ask for a redo

Could they maybe just replace the dark bullnose pieces with a white the same as the shower wall tile?

IMO the niche is only one item that doesn’t work for me I want to know how you plan to clean those tiles with the bevel . I don’t like niches at all but I think once it is filled with shampoo bottles it won’t matter I can’t tell waht the reason was for the marble at all.

True:

I think once it is filled with shampoo bottles it won’t matter.

It is hard to tell if that is a not so great job of doing the "frame" or if it is a not so good job at cleaning off the grout - can you see if any of that is just not wiped fully off vs it looking like a teriible cut corner??

You would have been better off with a square edged 3/4" thick piece of a nice white quartz. It will stick out just as much as the rise of the bevel tile . These pieces can be simply put together as a square corner or they can be mitered...

This was the best close up picture I could find.

I also feel like they could have laid the tile out different in the niche - instead of a 1/2 brick patter maybe do 1/3 .

Hope you can have this fixed to your liking....