2/3 cup cider vinegar
1-1/3 cup water
2 cups sugar
as much fresh mint as the pot will hold, or 7 spearmint teabags, whichever is handy.
Bring it all to a boil, and stir well to dissolve the sugar. Remove from heat. Let it steep in the pot overnight, chilled. Strain it the next day. Tint the resulting syrup with green (optional). When ready to serve, dilute it with water, one part syrup to 11 parts water.