That evidence lies in this, the Lycurgus cup. It’s an example of dichroic glass — that is, glass that takes on a different color depending on the light source. In this case, the opaque green ...
Lycurgus, King of the Edoni in Thrace, is ensnared by the nymph Ambrosia in the form of a vine. The famous Roman cup looks green when lit from outside but glows pink when lit from inside.