Those purple glass bottles are nice. They were originally clear and turned purple from years in the desert sun. They are called "desert glass". I believe only the glass made with magnesium will turn purple. 8)
SWR, You are right. Amethyst bottles are created from years of ultra-violet rays, such as in a desert. Large amounts of Manganese was used as a clarifier in glass from about 1880-1915. Here are some cool pics of colored bottles. http://www.keyshistory.org/shelfkeysbottlespage1.html