Hmm....could be your water? When we had a swimming pool, we added some water from our own well, that pool turned green, then brown, then purple (just like grape Koolaid) Every time the pool guy told us to try this or that chemical to fix it, the color changed. We finally got it right, but I think that certain minerals in your water can cause the color changes. Sometimes I notice a greenish ring in my white sink, but it cleans up easily. Grout is another story, much harder to clean. I am in the process of remodeling our bathroom, which has white grout and I will never choose white again. Too hard to keep nice and white. It looked great when we first put it in, but over the years it's been a hassle trying to keep it bright and white.

We have acidic well water but with a neutralizer system. When my neutralizer needs ot be serviced, I get staining like what you are seeing. Before you try any cleaning products, I recommend a water test. Check the yellow pages, see who can do a water test in your area and how to go about it. Here, I have to go pick up a kit which includes bottles and then fill them from the straight well water; before it hits my neutralizer system and water softener. Money well spent every other year or so just to make sure your water does not become contaminated with a neighbors runoff. If it is your water, left untreated it can eat through your pipes. If left untreated, you could have a much larger problem than stained grout. Once you determine whether it is your water or not, you can determine your course of action. If it is your well water, it will continue to re-occur until you deal with neutralizing your water.

First, your grout and mortar beneath the tile are not waterproof. Even a single grain of sand is porous. It will get wet and soak up water underneath your tile, so the mortar needs a mechanism to drain. I attached a photo so you can see near the drain pipe in the photo center lower edge and reference to "pea gravel to cover weep holes". Small weep holes exist to allow the MORTAR to drain as it will get wet - through the grout and even through the tile. Even the tile, whether ceramic or porcelain is NOT a waterproof surface (unless a glass-like glazed surface). You can see in this image, the shower pan liner is the waterproofing membrane going up the wall on the left and over the curb on the right. It also seals to the drain base. But above that base is the female threaded collar which accepts the upper section of drain. That female threaded collar has weep holes which should be covered with pea gravel so that mortar does not get into them while spreading mortar for the tiles. Different drain systems and styles have different mechanisms that allow the mortar beneath the tile to drain. Most of the shower water washes over the tile and grout and goes down the drain you see in the shower. But water also soaks through the grout and the mortar down to the waterproof membrane beneath that routes it to the drain assembly where the weep holes allow drainage. While excess water drains through weep holes, most will evaporate upward - the same way it entered the grout and mortar. The fact that you have a linear drain does not change this fact of shower drainage. Under your tiles exists a bed of mortar on top of some method of waterproofing. This bed of mortar MUST drain or it WILL fail. First the grout will discolor. Then the tiles will discolor. Then it will all come loose. Generally, people take their showers during one particular time of day, then the shower is unused until the following day. The mortar and grout will dry out during the downtime - certainly within a 24 hour period. Perhaps what you see is simply a grout discoloration from first-time-wet and it has changed color from its original. I would not be worried about the couple of softball sized wet areas. In a custom shower, especially if a mud pan was made, it is not unusual to have a low area here and there. It is hard to be 100% perfect with setting tile. But if the grout IS actually wet - there may be a problem. It should dry in a 24 hour period. From what I can see of the floor tile and wall tile - it looks like a fantastic job! No rookie did this. Bruce @ Elk Ridge Remodeling Co. 608.921.1074

UPDATE: The foreman came back with his lead plumber and another worker today. They removed the shower trim to check the valves from inside the shower and didn't see anything so they cut into the wall behind the shower to look at the pipes and valves. They found a leak from a loose connection between the pipes. (It was the pipe that goes to the handheld shower.) The plumber soldered the pipe. They are hoping that this is the fix to the leak. The team did not open the ceiling to look at the pan, drain, and plumbing since they found the leak in the other location. The foreman agreed to replace the ceiling though. I'm hopeful, but a couple of things seem odd. The leak happened after almost 6 months of use and the leak is not constant. It's only happened a few times even though we use the shower every day. Once we became aware of it, we noticed that it happens after the shower is turned off. Also, as I mentioned above, I noticed a wet area above the seam in the tiled shower entrance. Today, I noticed another wet area near the previous one and it I noticed it a couple of hours after the shower had been turned off (and after work had been done on the shower). Here are pictures of the plumbing and the new wet spot on the tile.