Galaxy Candy Apples

Wash and thoroughly dry 6 Granny Smith apples, then firmly push a wooden craft stick into the stem end of each apple until it feels secure.
Line a baking sheet with parchment paper and lightly coat it with nonstick cooking spray to ensure the apples don't stick after dipping.
Combine 1 cup granulated sugar, 1/2 cup light corn syrup, and 1/2 cup water in a medium heavy-bottomed saucepan. Cook over medium heat, stirring constantly with a wooden spoon, until the sugar completely dissolves and the mixture becomes clear, about 3-4 minutes.
Stop stirring and attach a candy thermometer to the side of the pan. Continue cooking without stirring until the mixture reaches 300°F (the hard crack stage), which should take about 15-20 minutes.
Immediately remove the pan from the heat and carefully whisk in 1 teaspoon vanilla extract, 1/4 teaspoon citric acid, 8 drops blue food coloring gel, and 4 drops purple food coloring gel until the color is evenly swirled, not fully blended.
Working quickly but carefully, tilt the pan and dip each apple into the hot candy coating, swirling to coat completely. Allow any excess to drip back into the pan.
Hold the coated apple over a separate bowl and immediately sprinkle with rainbow candy sprinkles and a light dusting of edible silver sparkle dust before the coating sets.
Place the finished apples on the prepared baking sheet and allow them to cool completely at room temperature for at least 1 hour until the candy coating is hard and crisp.