What was in a drink served on B.C. Street in Okinawa called a Rainbow?

I was stationed in Camp Hansen and we used to go out to this bar that served a drink called a Rainbow.It was poured over the back of a spoon,had several layers,had an anise/licorice type taste,and you would light it on fire and clap your hands over the glass,putting the flame out and then slam it.What was in this drink?I have heard it was opium based and or it was all or part absinthe.