Limestone turning orange

 

Hi - I hope someone can help me...We just bought a brand (http://maplered.com) new house about 4 months ago and (http://maplered.com) already the limeStone (http://g603.net) on our shower wall is turning orange. The limeStone (http://g603.net) was sealed twice before the shower was ever used. This is only happening to the bottom row of Tiles (http://www.g682.net) and (http://maplered.com) not all of them. The others looks like they have water marks on them. Is this normal? Our developer told us that this is just how limeStone (http://g603.net) wears in the shower when water hits it. If that were the case, wouldn't all the Tiles (http://www.g682.net) be turning orange? Please advise. Thanks!