Step 1: Prepare your apples by thoroughly washing and drying them to remove any wax or moisture. Insert a sturdy lollipop stick or wooden skewer into the stem end of each apple, about halfway through. Line a baking sheet with parchment paper or a silicone mat and lightly grease it with non-stick spray.
Step 2: In a heavy-bottomed saucepan, combine the granulated sugar, corn syrup, and water. Stir gently over medium heat until the sugar is completely dissolved. Once dissolved, stop stirring. Insert a candy thermometer, ensuring it doesn't touch the bottom of the pan. Continue to cook, without stirring, until the mixture reaches 300-310°F (149-154°C), the 'hard crack' stage.
Step 3: Carefully remove the hot syrup from the heat. Divide the hot syrup evenly into two separate heatproof bowls. Quickly add a good quality black gel food coloring to one bowl and a deep purple gel food coloring to the other. Stir just enough to incorporate the color evenly. Work swiftly as the syrup will begin to cool and thicken.
Step 4: Holding an apple by its stick, carefully dip it into one of the colored syrups. Swirl and rotate the apple to coat it completely. Lift the apple, allowing any excess syrup to drip back into the bowl, then gently twirl it for a few seconds for a smooth, even coating. Immediately transfer the coated apple to your prepared baking sheet. Repeat with the remaining apples, alternating between the black and purple syrups. While the candy is still wet, sprinkle with edible glitter or dust for extra glamour, if desired.
Step 5: Allow all dipped apples to cool completely and harden on the parchment paper. This usually takes about 20-30 minutes at room temperature. Resist touching them until they are firm and cool.