In a medium saucepan, combine the granulated sugar, corn syrup, and water. Stir over medium heat until the sugar dissolves completely. Bring the mixture to a boil and cook without stirring until it reaches 300°F (150°C) on a candy thermometer (hard crack stage).

Once the syrup has reached the desired temperature, remove it from the heat. Stir in the vanilla extract and citric acid (if using). Divide the syrup into separate bowls and add food coloring to each bowl.

Lightly dust a clean work surface with powdered sugar. Pour each colored syrup onto the surface, spreading it into thin layers about 1/8 inch thick. Let the syrup cool slightly but not harden completely.

Once the syrup layers are cool enough, stack the colors in a rainbow pattern. Starting from one end, roll the layers into a tight log, creating the candy roll.

Once the roll has cooled completely and hardened, use a sharp knife to slice it into bite-sized pieces.

Dust the candy rolls with powdered sugar to prevent them from sticking together. Serve the Rainbow Ribbon Candy Rolls as a fun treat!