It doesn't look bad and might look better when you grout it. The down side is it isn't right. Color variations will never go away and you will always see it. However, the is no reason to take the walls or the marfil out. Take out just the tiles that need to be replaced and put in the right tile. Better to do it now than for you to constantly question your decision making. Good luck.

Sounds like you didn't communicate your design/wishes very clearly with your tiling contractor - And didn't provide/select a material that had a finished edge to make these transitions.

I would stop, pull the niches and top of the curb out, and replace with a contrasting solid surfacing material can be built up on the edge to provide the thickness necessary for the transitions as well as finished edges...
...then use that same material as a countertop on your vanity so that it appears to be a deliberate design feature rather than an afterthought.

Hope you can get this fixed by one of the methods written about here. I don't think you're over reacting I'd be sick.

What is the name of the porcelanosa tile. Looks nice

it is Marmol Crema.

Communication is the most important thing when dealing with a contractor. I would agree with JM Design, you don't need to rip out the entire walls just the niche. Good luck!

Unless we arent understanding the entirity of whats going on.. there is no reason you should have to tear down anything aside from pulling out the offending tile. If they are telling you something different, they are either lying to you or we dont have the big picture.

There is a trim piece that matches the tile that can be used