1. Line a 9×5-inch loaf pan (or an 8×8-inch square pan) with foil or parchment paper and lightly spray with nonstick cooking spray. Set aside.
2. Prepare all ingredients and equipment before starting, as fudge sets quickly. You will need 3 bowls, 3 spatulas, food coloring, and a knife.
3. In a large saucepan, combine sugar, unsalted butter, and evaporated milk. Cook over medium heat, stirring frequently. When the mixture reaches a boil, stir continuously for 5 minutes to ensure proper cooking and avoid graininess.
4. Remove from heat and stir in marshmallow creme and white chocolate chips until the mixture is smooth and well combined.
5. Divide the fudge mixture evenly into three separate bowls. Add red gel food coloring to one bowl, blue gel food coloring to the second, and leave the third white. Stir each gently but thoroughly.
6. Pour the red layer into the prepared pan and smooth the top. Follow with the white layer, then finish with the blue layer. Stir each bowl just before pouring to prevent premature setting.
7. Use a knife to swirl through all three layers to create a marbled, tie-dye patriotic effect.
8. Optionally, sprinkle festive toppings such as red, white, and blue nonpareils or sprinkles on the top layer before the fudge sets for added texture and decoration.
9. Let the fudge cool completely at room temperature for at least 2 hours or refrigerate until fully set before cutting into pieces. For easier slicing, dip the knife in hot water and wipe dry between cuts.