the contractor put at least one coat of sealant on, but the marble seems to darken too easily with water. Sounds like the lighter the stone, the more sealant required?

Not necessarily. The best sealers on the market will be what's called "breatheable". Yes, they let moisture through, but the thing is they let it thru BOTH ways. Even with a sealer that's NOT breatheable, you're going to get moisture transmitting thru the grout. That's just the way it is. Sealer doesn't make grout waterproof. The problem is that it lets in thru slowly, and as a result the moisture becomes trapped for a much longer time, giving mold and mildew a chance to start. With a breatheable sealer, it doesn't impede the transference of moisture, so the grout, as well as under the tiles can dry out much more effectively and quickly, so as not to give mold and mildew a chance to get a start.

The bottom row of tile in the shower has turned permanently darker blue. I can't figure out if this is just that it is never fully drying out, and/or if the soap/water scum building up on the surface is trapping the water inside the tile?

As for this one, this is a real problem, and could become serious. What's happening is the shower pan is holding water, and it's whicking up the cement board behind the tile, almost like a sponge. Unlike a sponge, though, once the water gets above the top of the pan liner, it then finds a way out. You might want to check the bottoms of the walls that back up to the shower. You may be in for a very unpleasant surprise. If you do, email me, and I'll give you a number where I can be reached, because this could get complicated, and it WILL get expensive, unless you can get your contractor back to fix the problem, which would require complete demolition of the shower pan and bottom foot or 2 of all walls.

During a shower, tiles halfway up the wall look like they absorb some water in from the grout line (it kind of "bleeds" into the tile)

That's also to be expected with a breatheable sealer.

The mini floor tiles are also getting patches of discoloration, which seems to coincide with where water may be seeping in at cracked grout lines (where wall meets YIKES).

And now we're back to the pan holding water again, which I'm just about positive of. Yikes is right. I would start using another shower if you have one.

You know what, shoot me an email. Please.

Bill, thanks for quick response. Our contractor hasn't finished work yet, so we're going to escalate this issue immediately. We've asked about the sealant, but haven't specifically raised the water discoloration. And in the meantime use the kids' shower. The shower pan situation is what I'm nervous about. There isn't any visible damage anywhere on adjacent walls. We've only been in for a month, so not even that many showers to speak of. If we don't get a satisfactory response from contractor, will come back to you for more guidance. Thanks again.

I'll tell you exactly what he did and didn't do. He DIDN'T put a slope UNDER the pan membrane, which is one of the reasons why water is holding in the pan. The other reason is he didn't put in any kind of pea gravel or anything to keep the mud from clogging up the weepholes. This is why the floor tile is staying wet. The wall tile is getting wet because the cement board was installed low enough that the bottom of it is in the water that's holding in the pan. As for the preslope (under the pan memrbane) he's probably going to tell you that it's not necessary and all that. here's two different codes that says it is, and if that's not good enough for him, tell him to check the TCNA Handbook method b215 for shower receptors. It'll tell him the same thing.

IRC Preslope code:
2000 IRC:
P2709. 3 Installation. Lining materials shall be pitched one-fourth unit vertical in 12 units horizontal (2-percent slope) to weep holes in the subdrain by means of a smooth, solidly formed subbase, shall be properly recessed and fastened to ap-proved backing so as not to occupy the space required for the wall covering, and shall not be nailed or perforated at any point less than 1 inch (25. 4 mm) above the finished threshold.

Uniform Plumbing Code related to shower pan construction.

"412.8 When the construction of on-site built-up shower receptors is
permitted by the Administrative Authority, one of the following means shall
be employed:
(1) Shower receptors built directly on the ground:
Shower receptors built directly on the ground shall be watertight and shall
be constructed from approved type dense, non-absorbent and non-corrosive
materials. Each such receptor shall be adequately reinforced, shall be
provided with an approved flanged floor drain designed to make a watertight
joint in the floor, and shall have smooth, impervious, and durable surfaces.
(2) Shower receptors built above ground:
When shower receptors are built above ground the sub-floor and rough side of
walls to a height of not less than three (3) inches (76 mm) above the top of
the finished dam or threshold shall be first lined with sheet plastic*,
lead* or copper* or shall be lined with other durable and watertight
materials.
All lining materials shall be pitched one-quarter (1/4) inch per foot
(20.9 mm/m) to weep holes in the subdrain of a smooth and solidly formed
sub-base.