Your corners are the only place I really see issues that stand out. When we did our subway tile in the shower, we wrapped the tile around the corner, meaning the cut piece continued to the other wall, giving a more continual appearance. To me, it looks like he did each wall as a separate unit and just cut the ends when he got to them. Its not the way we would have done it (fairly experienced DIYers.) Colored grout will show more of the irregularities if the tile is at all wavy or imperfectly straight, or if your tiler didn't evenly space things. We chose white because we wanted the grout to disappear, and went with a tile at Lowes called American Olean that had small spacers built into the tile, so we just bumped each one up to the next and never had to worry about uneven installation. We dry fit our tile on the bottom to see where they would end up so we didn't get a tiny cut piece in the corner to have to deal with.
Hopefully he will agree to fix things. If not, and you are really unhappy with it, can't live with it, and taking it out isn't an option, you can minimize the effect that the colored grout would have on emphasizing the issues by using a white grout. That would help camouflage the things that stand out that you are seeing that bother you.
Heres what we did with our corners.
Best wishes to you....renos aren't always smooth sailing I know :) Hang in there.
Q
:)
Q