In a large bowl, melt the dark chocolate in the microwave in 20-second intervals, stirring in between each until smooth. Keep warm and set aside.
Divide the white chocolate into 2 separate medium bowls and melt in the microwave in 20-second intervals, stirring in between each until sooth. Add the blue food gel to one bowl and the purple food gel to the other and stir until your desired color is reached.
Line a baking sheet with parchment paper. Pour the dark chocolate on top, using a spatula to spread to your desired thickness.
Pour the blue chocolate over the dark chocolate, then add the purple chocolate. Use a knife or skewer to swirl the chocolate around until you get the desired look. Sprinkle with the star sprinkles. Refrigerate the chocolate for at least 2 hours before breaking into pieces.