Whisk together the gelatin and 3 tablespoons water in a small bowl and set aside to bloom.
Combine the sugar, corn syrup and 1/3 cup water in a medium saucepan, bring to a boil and cook until the sugar is dissolved and the mixture is clear, about 2 minutes. Remove from the heat and whisk in the bloomed gelatin to dissolve. Add the white chocolate and allow to sit 1 minute to melt. Add the condensed milk and combine with an immersion blender until emulsified and smooth.
Put 1/2 cup of the glaze into each of 3 small bowls. Using an immersion blender to combine (cleaning the blender attachment between each color), color one with the turquoise, one with the yellow and one with the white gel food coloring. Color the remaining glaze in the saucepan with the dark blue. Let cool to 95 degrees F, checking with an instant-read thermometer.
Starting at the center of the frozen frosted layer cake, pour the dark blue glaze over it. Drizzle with the remaining colors and swirl them together with a small spatula. Dust with edible glitter and allow to set in the refrigerator for 1 to 2 hours.
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