Line a half sheet pan with aluminum foil, making sure the foil is smooth.
Place the dark chocolate in a microwave-safe bowl. Heat at half-power in the microwave in 30-second intervals until the chocolate melts when stirred. Set aside.
Place the ruby chocolate in a separate microwave-safe bowl, and melt in the same way.
Spread the melted dark chocolate on the lined pan, making sure to create an even layer. Aim for about 1/4-inch thick.
Drizzle the melted ruby chocolate over the dark chocolate. Use a thin knife, a toothpick, or another implement to swirl the chocolates gently.
Sprinkle the candies and sprinkles over the swirled chocolates. They should stick to the wet chocolates, but you can press down lightly to adhere if needed.
Place the bark in the refrigerator until it's set. This should take about an hour.
Break the bark into pieces and serve or store.
Notes
*You can substitute white chocolate and an optional drop of red food coloring for a similar look. The flavor will be a bit different.
Store in an airtight container at room temperature or in the refrigerator up to 2 weeks.