Wash and dry the apples thoroughly, remove stems, and insert a wooden stick into the top of each apple. Place apples on a baking sheet lined with parchment paper. :contentReference[oaicite:0]{index=0}

In a saucepan, combine sugar, corn syrup and water. Heat over medium heat and stir until the sugar dissolves. :contentReference[oaicite:1]{index=1}

Bring the mixture to a boil without stirring. Cook until it reaches ~300 °F (hard-crack stage). :contentReference[oaicite:2]{index=2}

Remove from heat. Divide the hot candy syrup into separate bowls and tint each with a different gel food coloring to get rainbow colors. Add vanilla extract if using. :contentReference[oaicite:3]{index=3}

Working quickly, hold an apple by its stick and dip it into the colored syrup, twisting to coat evenly. For multicolor / rainbow-style coating, you can swirl multiple colors or dip sequentially. :contentReference[oaicite:4]{index=4}

Allow excess syrup to drip off, then place the coated apple on the parchment sheet. Let the candy coating harden completely at room temperature before serving. :contentReference[oaicite:5]{index=5}