Spray large mixing bowl lightly with cooking spray. Add popcorn, be sure to remove any unpopped kernels.
Spread plastic wrap on cookie sheet; set aside.
In medium saucepan, melt butter and marshmallows; stir until mixture is smooth. Stir in peppermint extract. Pour over popcorn, mixing until well coated. Let cool 2 minutes.
Spray hands with cooking spray and form popcorn mixture into 3-inch balls. Gently press colored sugar onto balls. Let sit on prepared cookie sheet until cool and set.