I have a new shower with 2X2s marble floor tile. Every time we take a shower an area of dark, wet looking tile and grout expands. Soon my entire floor will look that way. I've done some research and think that the drain weep holes may be clogged causing water accumulation to saturate my floor from beneath. My contractor thinks that as a result of me accidentally putting a nonpentrating sealer on the floor but then stripping it, is causing some water to seap in from the top and get trapped inside the tile therefore "staining" the floor. He wanted me to clog the drain and fill with water and see if entire floor changed to look wet which he thought would happen... no other tile got darketr. This leads me to believe it is coming from below the floor instead of the top. By the way, since stripping, I placed a tile enhancer/sealer on the floor. Any suggestions?

The people at johnbridge.com forum may be able to help you more. It can be so many things.
1) weep holes cloged up
2) no preslope under the shower pan
3) too much thin set between the tiles before the grout went down.

This happened to me also. I bought some grout stain and colored the grout see c-cure.com for grout colorant. Now I just don't care anymore. There was really no way to get the people who did the work back here... The colored grout stain also acts as a sealer and it is pretty tuff.

Also colored grout has a tendency to loose color anyway. It is a real PITA. I hate grout!

Tom