01 - Combine finely chopped white chocolate in a heatproof mixing bowl.
02 - Heat heavy cream and unsalted butter in a small saucepan over medium heat until just simmering. Pour the hot cream mixture over the chocolate and let stand for 2 minutes. Stir gently until completely smooth and glossy.
03 - Stir in vanilla extract and a pinch of salt until fully integrated.
04 - Portion the mixture equally into three bowls. Add red gel coloring and crushed freeze-dried raspberries to one bowl, blue gel coloring and crushed freeze-dried blueberries to a second bowl, and leave the third natural for the white layer. Mix each until uniform in color.
05 - Place all three bowls in the refrigerator for 45 minutes, or until the mixtures are firm enough to scoop.
06 - Using a truffle scoop or teaspoon, take 1/2 teaspoon from each colored mixture. Press together and roll gently between your palms to achieve a marbled tricolor ball. Repeat until all mixture is used.
07 - Roll each truffle in white sprinkles or sanding sugar for a decorative finish.
08 - Arrange truffles on a parchment-lined baking sheet and refrigerate for 20 minutes before serving to set. Keep chilled until ready to serve.