This is something that has recently been turning up and needs to be addressed.
I've listed these pieces here as an Alteration. The reason being, these pieces were never
made in this color during the Victorian era. There is a process by which authentic early Opalescent
glass pieces are placed in a box and exposed to UV light for an extended period of time. This causes
the glass to turn purple or Amethyst. The color change is not caused from sunlight although
this type of glass is called Sun Purpled glass. It's not known who is doing it, but
they are taking old authentic patterns in Opalescent Glass and turning them purple by this
process. The piece shown on the left is called Many Loops, and the piece on the right is
called Calyx. So far these are the only two patterns that I've seen "Color Altered" this way.
The safe bet now for collectors, is to stick to the known patterns that were made in
Amethyst Opalescent. If other patterns surface with altered colors, they will be added here.
If you are not sure about purchasing something in this color, the safe bet is to ask first.