Manganese was used as a decoloring agent prior to 1915 or so... you will find discussion of this elsewhere in this forum. Bottles with manganese will turn a purple-ish color when exposed to sun, or, in more recent times, to strong UV light sources.
This is a ketchup or food sauce bottle from the very early 20th century.
To answer your other question, "Do fakes have value?" - there are lots of examples of reproductions, replicas or modern bottles made in an old style which do have some decent value. A classic example are the EG Booz cabin whiskey bottles. Even the reproductions can bring hundreds of dollars.