Who's installing? I installed my own porcelain 12x24 and it was very difficult for me. I have the dreaded lipage. If you are going to have a pro install, make sure they know what they are in for. I had lots of help from some old GW posters. Couldn't have done it without their help. But I would never recommend laying anything larger than 12x12 for novice tilers, after my experience.

Now as far as color. I just say what ever you like. Things tend to be very light these days. But the picture you show is beautiful. I couldn't get the link to open so I don't know the material, thinking it might be marble due to your comment about concrete. If it is marble, it does absorb water. and many people have had nightmares with shower pans, tiled with marble. But those issues seem to be a poorly built base. Then the water doesn't drain under the tiles, to the drain, and causes constant wet look, and staining, especially light marble. I would recommend porcelain for all parts of the shower. I also would recommend to have a solid surface base that is pre slopped if you are DIYing it. I used a 3x5' Kohler cast iron base and have been very happy with it. I don't have to worry about the function of the drainage. I went with the cast iron, cause I was DIYing my shower and I didn't want to tackle the shower base slope construction. If I had a fail, it would be on me and I'd have to take it out.

I just got the link open, my computer wifi is acting up. I see that it's porcelain. It is a good way to go, porcelain if very durable, very low water permeability, and can come in so many beautiful designs these days. Its the way to go IMHO. But I would not recommend that size unless a pro, and a good pro were to install it.

It is lovely! And very expensive, one wall would cost close to $700, if I am doing my math correctly.

Thanks so much @enduring! We have zero DYI skills so this will be 100% pros. But I'm conscious of keeping things as practical and uncomplicated as possible, especially because we'll have 3 full baths to do. This would be for the master bath shower, which seems like the one place to consider a small splurge. OTOH I realize that this may not look as sleek for our setup, where the shower base is 4' wide but there's also a 16" bench built-in. Something to ponder.

Thanks to your posts I'm also going down the shower pan rabbit hole (seems like another way to keep things less complicated and avoid opportunities for errors etc.) Of the 3 baths, I think only the hall bath might work for a Kohler shower base simply because our sizes are a bit irregular.

You can have solid surface custom made. But your porcelain, if installed on a good pre-slope would be lovely. There are a lot of systems available. Schluter, being one of many. It has a good reputation.