I have the lid to that decanter that you posted a link to (specifically, THIS ONE:)http://i20.photobucket.com/albums/b217/lustrousstone/IMG_0408.jpg
AND my cup in the daylight, bright sunlight (106 F today!) is an exact match!
( I once had a decanter and two lids, but sold it off, but kept one lid just for the color sample).
Having said that, I also have a piece of sunshine amber by Webb in my collection, and this cup is darker amber than Webb's sunshine amber.
I am thinking continental Europe also, most likely Bohemian.
The thing that surprises me most about this piece is it's weight! 11.45 oz (345grams) is heavy for a cup that is not 5" tall!
Thanks for digging up that thread, to remind me to compare it to the stopper I have. Indoors, the piece looks amber. Outdoors (under the UV of the sun), it is more of a deep olive color.