I'd say chrome. White might clash with the white tile if it's a different white. Black might stick out too much depending on how much schluter will there be? I find it just kind of blends in if done right. Maybe even the brushed nickel would work, I'm trying to think of what I see around here. I think brushed is everywhere and I hardly notice it (like in show homes, etc)

Is the 1st pic you posted an inspiration pic? If so, I would recommend black. The standout feature of that bath, for me, is the strong black lines of the shower frame, the edging of the vanity, and around the mirror. Black tile liner would be a different path to a similar effect.

I'm using the same tile and a white trim in the other bathroom, so it disappears. It's as close as the tile colour as you can get.

To be clear, there's no wood in the shower, the window is vinyl, and the whole surround will be tiled. I just need something where the tile turns "90" degrees (not actually 90 due to the slope). A metal edge to hide the edge of the tile.

And yes, the first pic is an inspiration, although I'm not sure how close I can get with chrome fixtures, and no wood. :( But I do have the black window frame and black light fixture.

It's not plastic, it's metal. And bullnose isn't available.

I am aware it comes in PVC. I don't want PVC. The stuff I am getting is metal.

ETA: Holy poop! $7 for the PVC is crazy! It's about $5 at the Home Depot here, and our prices are usually much higher than in the US, and even cheaper through my tile shop than HD or Lowes.