Make a ganache. In a non-reactive double boiler set over medium-low heat, bring the cream, sugar, and butter to a boil. Meanwhile, chop the chocolate into small chunks - a serrated knife works best for this.
Add the chocolate chunks to the cream mixture in the double boiler, whisking, until it is melted and incorporated into the cream. Finally, add the food coloring until it is the desired shade of green.
Keep mixture warm in a fondue pot near the door. Set out the fruit and the pretzels for dipping with long wooden skewers next to the fondue pot. Guests can dip their pretzels or fruit into the fondue and then roll them in the candy sprinkles, if desired.
