How about TEC XT? Comes in both Sanded and Unsanded versions (for most colors), and is supposed to be more stain resistant and mold and mildew resistant than other cement-based grouts. It does require a longer cure time 7-10 days before getting wet or sealing (doesn't need to be sealed, but can be, with a solvent-based sealer, which we did when we sealed the marble and trav tile in both bathrooms). I sealed it in the MB at 7 days because I needed that bathroom functional "now" LOL. It also requires a drier clean-up (just wring sponge out well when wiping off excess grout, according to the rep with whom I spoke during my grout "research"--there's a video you can watch, too). It's a little stickier than the reg TEC grout, so you might need a bit more elbow grease to remove grout haze, but that's about it. We used the Bright White for the field tile in both upstairs baths (used the reg TEC in Bright White for our kitchen and guest bathroom since the XT either wasn't around then or we just didn't know about it at the time). We used both the Sanded and the Unsanded. The Unsanded is a bit whiter than the Sanded (because the sanded has actual grains of sand, which I'm sure you know), but both seem white enough. We used a very glossy, very white, Porcelanosa large format tile in the MB. Our grout lines are very tight, except for the White Thassos mosaic/border (which came pre-mounted on mesh), and the Unsanded worked very well. We also used it (in Almond) with the split faced trav mosaic in the hall bath which had practically non-existent grout lines in spots. Of course, when I say "we" used any of these products, I mean our wonderful tile guys used them for us!

Here's my latest response from my GC on how the shower was installed and his thoughts on fixing the project. ========================== The Shower pan was installed with a pre-slope. A positive weep hole protector was used during installation. The waterproofing system is a 30 mil pan liner that extends up the walls 18" on all sides. I did ask the tile installer about the typical time for a shower pan to dry out, 24 hours is not unreasonable, but 5 days is not typical. If the discoloration is caused by persistent moisture there is something not functioning properly. That being said, he is very confident in the installation of the pan liner and was personally on site while the work was being completed. He feels the discoloration is likely not related to the Pan holding water. However, we will reserve judgment until we have had a chance to inspect the shower together. "Assuming" we do not have a problem with the pan draining. One Idea our tile installer offered would be to replace the grout in the floor with an epoxy grout. Epoxy grout is going to discolor less with moisture, if we remove all of the existing grout on the floor we should get a more consistent color when we regrout, and epoxy grout will allow less water to penetrate through the finished surface to the pan liner. Of course, first we have to be sure that everything is working as designed. ======================

Reading here at GardenWeb, I know that tile and grout are not waterproof. Your guy is just not informed. Yes, we have bathrooms done "the old way" and sometimes the tile above the bathtub did stay for many years. But how many have rotten walls and floors behind them? Do yourself a favor and read up on how a shower should be built before you hire the next person, and talk about their methods and products before you hire. People are still out there, putting up materials worth thousands of dollars, not knowing what they are doing. After the leaks ruin other rooms in the house, all has to be torn out and redone. It happens all the time. Here is a current thread: http://ths.gardenweb.com/discussions/4654503/wall-underlayment-for-shower-best-practice?n=4

Corian and other solid surface. Fiberglass reinforced plastic. Large format tile.