To me this sort of decision has to be partly informed by how much of the tile will have to be cut and how good your tile setter is at cutting tile.

For me, if doing all these accents means a lot of tile with cut edges I would be hesitant. I don't like the way cut edges of tile look out in the middle of the field, and the use of accents and of standard niches for that matter usually mean there is a lot of cutting of tiles to fit in the accent tiles.

Does this make sense? But I won't (voluntarily) use standard niches that require tiles to be cut around the niche, either. I will figure out what size the niche has to be to be surrounded by all full tile with bullnose. It's a pain. And it can't be done with a typical subway layout because brick patterns always require a cut tile for every full tile at the end of a run anyway. (I am on the lookout for the company that offers 3x3 standard to make the half-tile for their standard 6x3 layout. I just finished a bathroom that has about 12 fully "cut" tiles, and one row of slightly shaved tiles in the whole bathroom--and it's 2x2 tile. The plan was to have the entire bathroom be 100% full tiles, and we didn't quite make it. And I stare at the row of shaved tiles when I am taking a shower. But this isn't really answering your question.

I personally don't think a bathroom with that many sizes of tile even if they were all the same color would look bland or sterile.

I think if you start to "accent" too many things, it's no longer an accent.

I would be against too many accent areas if it wreaked havoc with the overall tile layout.

Nothing personal against decorative painters, I nearly got an MFA in painting as my alternate degree instead of interior design as my alternate degree, but having known some and having been in the houses of some (and having unearthed some of the paint combinations covered up by staging-khaki paint in a house Owned by one:

My impression is that a lot of decorative painters don't know when to stop and someone has to tell them when to stop--and this isn't always easy when they are on a design job.

But really, if I had a decorative painter in my house, I would want the bathroom tile to be all white and I would want the decorative painter to Paint the walls in a mural or something decorative.

Here is subway/herringbone patterns in one shower.

{{gwi:2133620}}

And this is the accent tile in the corners like he's thinking.

{{gwi:2133621}}

And this is the accent tile. But in the 2x4 brick pattern

{{gwi:2133622}}

I should've specified. He's a custom airbrush and automotive painter.

This is a mixer he did for a customer recently.
{{gwi:2133623}}

I think his plan was to run the accents vertically to avoid excess cuts on the back wall. And not full sheets but half sheets.

He is trying to use up as much of the tile as possible since it was expensive. I'm not as worried about the cost as I am the final look.

Would the herringbone be banded by the accent as well?

What is the ratio of field to accent going to be? If there's accent in the corners and then around the panels and in the niche, it may start to take over the field tile because that's not an oversized shower.

I like the mixer a lot.

Can you reload the first two photos? They aren't showing for me.

Did you mean you want to put the glass tiles inside the niche? You might want to reconsider because once the niche is full of stuff, you won't see much of the glass tiles.

Here's photo 1

I not matter what want the accent glass in the niches. We've done it before in other bathrooms and love the look. We don't use a lot of products so it won't be loaded up.

Photo2

He wants to band the accent with cigar piping. The herringbone wouldn't be banded. It would be floor to ceiling approx 4.5' of the back wall with 6" either side floor to ceiling accent. Essentially like this picture.

Cigar piping around the control wall accents and around the niches.

I don't like tile, but I do love the herringbone pattern. I would not add anything else to it. I do not like the photo of the black and grey tile, to busy for me.

What design did you choose in the end?