I have no experience with this, but my thinking is that darker tile often equals darker grout. Darker grout equals less noticeable dirt on the grout lines. Lighter colored grouts are much harder to keep looking clean and nice in a shower. So dark might be a good way to go.

Unfortunately, I don't have any pics, but I just did a shower the end of last week where the shower floor was a chocolate brown 1x1 with matching grout, and it really looked nice. The walls were an "autumn medley" of colors in 2x2, with a nice sainless Kerdi drain in the middle. :-) Very nice.

Have your setter prepare a test board with your grout colour. Bill is a master setter - many are not.

Too many jobs look like trash because the dark grout washes out and looks pail and discoloured because of multiple reasons.

Research the subject "Not Happy With My Grout Colour" "Black grout looks Gray" etc. The web is filled with sad sad stories.

The test board doesn't need to be huge and can aid you in grout spacing, grout colour choice and sealers.

One of my favourite floors is a Black marble 4"x4" with White subway border detail.

So we should make allowances for those who can't do their job properly?

Sorry-- I disagree.

I have a friend with a solid brown shower floor. YES you can easily see the soap scum and water deposits. She is a good housekeeper with a cleaning service several times a month. The shower is in the guest bathroom, so it has not seen lots of wear.

I think this is something you have to consider. Bill if I hire you to set my black floor and black tile shower floor I'm sure it will turn out perfect, I know you would build a waterproof floor and away we go.

Now let's say we have Mr. Hubby setting his third bathroom project, he has been to the box store twice for "Training" and is going to do the same job. What are the odds he uses a cheap grout? What are the odds the grout is not mix right? What are the odds he uses too much water cleaning the sponge? What are the odds he doesn't let the grout set up enough? And on and on...

Lets pretend it is a white subway tile job with white grout - much less difficult job and if the Hubby goes South a little the ill effects will be hard to see on a white on white job.

Lets just for fun say you make Mr. Hubby, Steve, Bob or who ever you pick to do a test board. Here you can see the finished project. I think you have to factor this into the equation.

Search the web - I think 1 out of 7 posts on JB's site is about this problem - it is a problem - that is for sure.

In my experience light colors tend to show dirt, and very dark colors tend to get disclored from hard water deposits. For the lazier housekeepers (like me!) a more mid-range color works best.
It's like cars - which cars look worse between washes? Beige cars or black cars?

John, a DIYer is one thing. But if someone hires another pro to do the job, he DAMN well better be able to grout a damn shower floor, properly. If not, I'd be willing to bet you'll have much bigger problems than discolored grout. ANY so called pro should be able to grout a tile installation. You don't need to be in the trade for centuries like me. :-)

A little story that I think is very appropriate-- When my stepson Adam first started in the trade, at the time, we were going all over new England tiling Wendys, Tim Hortons, and 99 Restaurants and Pubs. (The ironic thing is this is about grouting, too) We were working on this 99 in Saratoga Springs, New York, and I'd put him working on grouting the wall tile in one of the bathrooms (standard 4 1/4" wall tile with unsanded grout). I came in and he THOUGHT he was about halfway done, and I went ballistic on him. Nevermind grout haze, there were actual grout SMEARS still on the wall, almost hardening as we watched. His reply to me was that he hadn't been in the trade for 20 something years, and I shouldn't expect the same level of work from him that I expect from myself. My answer to him then was the same as it is to you now. I didn't come out the "chute" with a grout float in one hand and a notch trowel in the other. I didn't just all of the sudden "have it", either. One of the first things I learned was how to grout clean and flush.

The difference between someone like me, and any old installer is it might take the installer a little more time, but I'd expect (AND ACCEPT) no less quality.