Hi M.,
We had a major mold problem due to builder error in our master bathroom which lead to a mold remedial company (Belfor-outstanding company!) to come out and gut our bathroom and rest of the house where the mold has spread. We also hired an environmental company to come out and count mold spores in the air, etc. The only reason I am telling you this is because I have learned alot about mold during this process. We redid our shower and tub with mold resistant grout, much more expensive than regular and a pain to install, but we hired someone to do that. It is the best thing ever. As far as your question about the caulk itself, I so know what you are talking about. At Century tile, they sell higher end caulk in several different colors to match your tile, etc. It is about $20.00 for a bottle, but it has been almost a year and we have not had a problem with the caulk looking dirty or anything. For me, the $20.00 was not a huge deal, yes it is alot more than the stuff at Home Depot, but it is worth it! Also, if you do not want to do it yourself, Grout Medic charges $120.00 to do this, which is alot, but than it is done...... ###-###-####‎ and Kevin Ferrara came out the same day to talk with us about options, etc. I hope this helps. If you have other specific questions, just e-mail me.
Good luck :)
Jennifer