01 - Line a large baking sheet with parchment paper or a silicone mat. Insert a wooden stick firmly into the stem end of each apple, ensuring it's secure for dipping.
02 - In a heavy-bottomed saucepan, combine granulated sugar, water, and light corn syrup. Place over medium heat and stir continuously until the sugar completely dissolves and the mixture is clear.
03 - Increase heat to high and bring to a rolling boil. Stop stirring entirely. Attach a candy thermometer and cook until syrup reaches exactly 300°F (hard crack stage). Remove from heat immediately to prevent burning.
04 - Stir in vanilla extract if using. Quickly add several drops of red, blue, and white gel food coloring directly into the hot syrup. Gently swirl with a wooden skewer just once or twice—do not fully incorporate. You want distinct streaks of color visible throughout.
05 - Working swiftly before syrup thickens, hold an apple by the stick and dip it completely into the candy mixture. Rotate and tilt to ensure full coverage, allowing excess syrup to drip back into the pan. The swirling motion during dipping enhances the marbled pattern.
06 - Place coated apple on prepared baking sheet. Repeat with remaining apples, giving the syrup a brief, gentle swirl between each dip to redistribute colors. Work quickly as syrup will thicken as it cools.
07 - Allow apples to rest undisturbed at room temperature for approximately 15 minutes until the candy shell is completely hard and glossy. Do not refrigerate as condensation can ruin the finish.