Answer from a Local.
You most probably had a PISTACCHIELLO (made from pistachio) , is common sense here in milan, after you are having a classic neapolitan pizza , that you are given 3 bootles of liqueur, and you can pour it as much as you want.
They usually came in these colors :
- yellow (limoncello from lemons)
- green (PISTACCHIELLO from pistachio)
- orange (MELONCELLO from cantaloupe)
i'm pretty sure you are you do not remember very well the colours as described earlier, but if your favourite was the cantaloupe one was the orange, otherwise it was PISTACCHIELLO.
That said, i don't know if there is request for this product outside milan and amalfi coast, try searching on google for
PISTACCHIELLO
MELONCELLO.