For those who don't care to be held hostage by the journalist as he forces you through a long winded narrative: gold and silver nano particles are embedded into the glass

I wonder if the more accurate title might be: Scientists Discover How Ancient Romas Made Color-Changing Glass. Meaning that I've seen many examples of glass that appears different colors under different circumstances, but apparently none that worked the way this cup does.

The Romans appreciated much more the jewels with variable colors than those with fixed colors.

Those among opals and pearls that exhibited a very strong play of colors, due to diffraction, were valued far above the gems with fixed color, like emeralds and rubies.

Thus it is likely that this kind of glass, with different colors in transmitted and reflected light, was very expensive, so it is not surprising that in TFA a letter of one of the Roman emperors is cited, where he mentions receiving such cups as a gift, because they certainly would have been considered a gift worthy of an emperor.

The ancient artefact described also featured in a Jonathon Blow lecture, as an example of an engineering skill we lost for 1600 years: https://youtu.be/ZSRHeXYDLko?t=402