In a mixing bowl, combine the instant pistachio pudding mix and buttermilk.
Whisk the mixture until smooth and well blended.
Gently fold in the drained crushed pineapple.
Add the mini marshmallows and stir to combine.
Incorporate the whipped topping until fully combined.
Mix in the chopped pecans for a crunchy texture.
If desired, add a few drops of green food coloring.
Transfer the mixture to a serving bowl or individual cups.
Garnish with halved maraschino cherries and additional pecans.
Chill in the refrigerator for at least 1 hour before serving.