rocks & plant pots in tank

Limestone will slowly disolve in an aquarium. Test you rocks by
dripping some vinegar on them. If you see fizzing, it's best not to
add the rock.

Terra Cota (orange plant containers) have been used for years in
aquariums for caves in cichlid aquariums as breeding caves. These are
'clay' type plots and yours may have just had some dust. I'd rinse it
a few more times, if you still see orange, you may want to by
different pot - probably get better quality from a local nursery.