wall tile darkens when wet

The lowest course of wall tile at the rear of the shower won't dry out with daily use and is dark.
This is a newly constructed mud shower pan and enclosure. There is 12x12 marble tile on the shower walls, and 2x2 marble on the shower floor. The marble has been sealed, the drain weep holes open, pre-pour mud/liner- sloped well etc. It seems that its getting wet fromt the back.
Is this a construction problem in addtition to aesthetic?
Thanks!
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On Jul 11, 11:19 am, snipped-for-privacy@adelphia.net wrote:

try bleach to see if its mold
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nah, it's brand new and gets lighter when not in use over time.
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snipped-for-privacy@adelphia.net wrote:

have is windowsills, and they have marks from wet glasses. Marble is pretty porous, so it sure sounds like it is ablsorbing water and/or soap. Water would hit with more force, perhaps, and soak in more there???? I'm confused at the popularity of marble for showers and floors, because all I have read about it cautions agains standing water.
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