Blck ring around bottles in my shower

[refuge821]

I have noticed one particular shampoo that leaves a black ring under it ... kinda purplish.  It has made me wonder if there's some chemical in it that is not a good thing.  I've used natural hair care products from the health food store for a very long time, but this last batch of shampoo I bought has been doing this.  Maybe it's the same thing ... if all your items can relate to something like that. 

[brutus101]

I am not sure if walls or ceiling has been treated.

[Thomas Rich]

 I know that the apt above had a serious water damage.  I am having black rings around bottles in my shower (shampoo, bubble bath and even a sponge)  Do I have mold as a result of maybe the walls or ceiling not treated?