Wash and thoroughly dry the grapes, then arrange them on a clean plate.

In a medium saucepan, combine granulated sugar, water, and light corn syrup. Heat over medium, stirring until the sugar dissolves. Bring to a boil for 5-7 minutes until glossy.

Reduce heat and divide syrup into separate bowls. Add white gel food coloring to one, and pink and blue food coloring to the others, mixing until desired colors are achieved.

Dip each grape into the colored syrup, swirling gently to create a marbled effect. Repeat until all grapes are coated.

Transfer the coated grapes to parchment paper to set for about 30 minutes or until the candy shell hardens.