Place 3 tablespoons of water in a small bowl and whisk in the gelatin. Set aside to bloom for a few minutes.
Combine the sugar, corn syrup and 1/3 cup water in a medium saucepan. Bring to a boil and cook, stirring, until the sugar is dissolved and the mixture is clear, about 2 minutes. Remove from the heat and whisk in the bloomed gelatin, whisking until dissolved. Add the white chocolate and allow to sit 1 minute to melt. Add the condensed milk and 1 teaspoon of white gel food coloring. Combine with an immersion blender until emulsified and smooth. Let cool until the mixture registers 100 degrees F on an instant-read thermometer.
Divide the glaze evenly among 3 small bowls. Using an immersion blender, add 3 drops of fuchsia food coloring to the first bowl and combine. Add 4 drops of purple food coloring to the second bowl and combine. Add 5 drops of blue food coloring to the third bowl and combine. The temperature of the colored glazes should be 95 degrees F before pouring.
Place your frozen frosted cake on top of an inverted cake pan resting on top of a baking sheet lined with a cooling rack. Starting at the center of the cake, pour the glazes over it, alternating to swirl the colors. Use a small offset spatula to create more swirls if desired. Dust with flakes of gold leaf. Refrigerate the cake for 1 to 2 hours before serving.