Pop your popcorn and remove any unpopped kernels. Place the popped popcorn in a large greased bowl and keep warm in a 250°F oven.
In a medium saucepan, combine sugar, corn syrup, water, and salt. Cook over medium heat, stirring constantly, until the mixture comes to a boil.
Continue cooking without stirring until the mixture reaches 250°F on a candy thermometer (hard ball stage), about 5-7 minutes.
Remove from heat and stir in butter and vanilla extract. Add food coloring if desired.
Pour the hot syrup over the warm popcorn and stir quickly to coat evenly.
When cool enough to handle, butter your hands generously and quickly shape the mixture into 3-inch balls, pressing firmly so they hold together.
Place on wax paper to cool completely. Wrap in cellophane or plastic wrap for gift-giving or storage.